At present there is much discussion of a potential "no fly zone" being imposed over Libya.
We shall discuss some practicalities of that here.
A more expert analysis may be found on Sharkey Ward's blog.
Libya is a very large country,in order to maintain a no fly zone there it will be necessary to patrol a number of areas in the country.
Here we will only consider the resources needed to patrol over Tripoli from Akrotiri.
British aircraft carriers have in the past operated as close as 50 miles from enemy held coastlines.
American carriers often stay further out,one might expect an American carrier to be 125 miles out in the Gulf of Sidra,about 15 minutes flying time from the Libyan coast.
With David Cameron having taken the decision to retire the Royal Navy's (R.N.) carrier capability,British aircraft are expected to operate from the Royal Air Force (R.A.F.) base at Akrotiri on Cyprus.
It is approximately 1,150 miles from Akrotiri to the Libyan capital Tripoli.
The "Tyranny of Distance" dictates that such long distances have a significant impact on the resources required to enforce a "No Fly Zone" (N.F.Z.) over Libya.
Aircraft have finite unrefueled endurance,about 3 hours in the case of a Typhoon.
The greater the distance between their base and the operational area the greater the time spent in transit and the shorter the time the aircraft can spend on station without aerial refueling.
This in turn means that as the range between the base and the operating area increases so does the number of aircraft which are required to maintain a combat air patrol.
The above graph shows the number of aircraft required to maintain a single aircraft on station around the clock and the endurance on station of each aircraft.
It assumes each aircraft flies 1 unrefuelled sortie per day of 3 hours endurance at 500 miles per hour.
These figures are fairly typical of modern fighter aircraft.
Some Basic Assumptions
There are many variables in working out an aircraft's refueling requirements,fuel burn varies as the aircraft becomes lighter as a result of consuming it's weight of fuel.
To simplify things for the purpose of this discussion we shall henceforth work on the basis that a Typhoon has 3 hours endurance on a capacity of 9 tonnes of fuel with a fuel burn of 3 tonnes per hour at a speed of 500 miles per hour.
For simplicity,we shall also ignore fuel reserves and time spent refuelling.
This will tend understate the number of refuelling "hook ups" and fuel transfer required.
This will tend understate the number of refuelling "hook ups" and fuel transfer required.
This will not be accurate but it will be adequate for illustrative purposes.
3 Hour Sorties
As the round trip from Akrotiri to Tripoli will take about 5 hours and the unrefueled endurance of a Typhoon is about 3 hours,a Typhoon cannot fly from Akrotiri to Tripoli and back without aerial refueling.
6 Hour Sorties
As the round trip from Akrotiri to Tripoli will take about 5 hours,a Typhoon cannot fly that far without aerial refueling.
A complete refueling including about 9 tonnes of fuel would extend the Typhoon's endurance to approximately 6 hours,giving 1 hour on station over Tripoli if the aircraft was based at Akrotiri.
To maintain a single Typhoon on patrol over Tripoli around the clock would require 24 6 hour long Typhoon sorties.
As a combat patrol is usually flown by a pair of aircraft,it would require 48 6 hour long Typhoon sorties to keep a pair of Akrotiri based Typhoons over Tripoli.
This would entail 432 tonnes of aerial fuel transfer per day and 48 aerial refueling "hook ups" per day.
9 Hour Sorties
If each aircraft received 2 complete refuelings per sortie,totaling 18 tonnes of aerial fuel transfer per sortie,it's endurance would be extended to about 9 hours giving 4 hours on station over Tripoli per sortie.
This would require 6 daily Typhoon sorties to keep a single aircraft over Tripoli or 12 daily sorties to keep a pair of aircraft over the Libyan capital.
These 12 Typhoon sorties would between them require 24 aerial refuellings totalling 216 tonnes of fuel transfer each day.
12 Hour Sorties
If each aircraft received 3 complete refuelings per sortie,totaling 27 tonnes of aerial fuel transfer per sortie,it's endurance would be extended to about 12 hours giving 7 hours on station over Tripoli per sortie.
This would require less than 3.5 daily Typhoon sorties (actually about 3.5) to keep a single aircraft over Tripoli or 7 daily sorties to keep a pair of aircraft over the Libyan capital.
These 7 Typhoon sorties would between them require 21 aerial refuellings totalling 189 tonnes of fuel transfer each day.
Sortie Rates
The number of aircraft required to generate these sorties depends on a number of factors.
Longer sorties require the aircraft to spend more time in the air and on the ground undergoing maintenance between sorties.
Consequently increasing the sortie length results in each aircraft flying fewer sorties each day.
Different aircraft require different amounts of maintenance between sorties and so some aircraft types will be able to generate fewer sorties than others.
Some air arms tend to generate higher sortie rates than others,the Royal Air Force tends to generate far fewer sorties per aircraft per day than either the Fleet Air Arm or foreign air arms.
The following historical examples of recent fast jet operations may give some indication of how many daily sorties the Typhoon fleet might generate:
During the Falklands War in 1982 the Fleet Air Arm's Sea Harriers averaged over 1.4 sorties per aircraft per day each of which was of less than 2 hours endurance;
During the Invasion of Afghanistan in 2001 the United States Navy's F18s averaged about 1.1 sortie per aircraft per day each of which was typically of 4.5 hours endurance and some of which lasted up to 11 hours;
In Afghanistan today,British Tornados average about 0.7 sorties per aircraft per day flying sorties which typically last 3-4 hours;
During the bombing of Kosovo in 1999,the Royal Air Force's Tornados and Harriers averaged about 0.5 sorties per aircraft per day while flying from bases which ranged from 250 miles from central Kosovo to over 900 miles from central Kosovo for the Bruggen based Tornados which often flew sorties of 7 hours endurance;
During the Invasion of Afghanistan in 2001 the United States Air Force's 12 F15Es of the 391st Fighter Squadron flying from Ahmed Al Jaber in Kuwait,1,500 miles from Kabul,averaged about 0.25 sorties per aircraft per day with an average sortie length of 10 hours,some of these sorties lasted over 15 hours,the longest fighter sorties in history.
Based on these and other historic figures we will make the following estimates for the Typhoon fleet:
An average of 0.8 sorties per aircraft per day of 3 hours endurance per sortie;
An average of 0.6 sorties per aircraft per day of 6 hours endurance per sortie;
An average of 0.4 sorties per aircraft per day of 9 hours endurance per sortie;
An average of 0.2 sorties per aircraft per day of 12 hours endurance per sortie.
Aircraft Requirement
By combining these sortie rate estimates with our estimates of how many Typhoon sorties are required to keep an Akrotiri based Typhoon over Tripoli,we get the following estimates for the number of aircraft required in each case.
When flying 3 hour sorties it is not possible to sustain 2 Typhoons on patrol over Tripoli.
When flying 6 hour sorties 80 Typhoons will be required to sustain 2 on patrol over Tripoli.
When flying 9 hour sorties 30 Typhoons will be required to sustain 2 on patrol over Tripoli.
When flying 12 hour sorties 35 Typhoons will be required to sustain 2 on patrol over Tripoli.
Aircraft Available
The Royal Air Force Typhoon fleet consists of 3 frontline squadrons,each of which now appears to have 12 aircraft (the number of aircraft in each Typhoons squadron was at one time expected to be 17).
There is also a flight of 4 Typhoons defending the Falkland Islands.
Typhoons provide North and South Quick Reaction Alert in the United Kingdom.
This requires at least 2 of these 3 squadrons.
This leaves a single frontline Typhoon Squadron of 12 aircraft which may be available for deployment to Akrotiri.
This is not sufficient to provide the number of Typhoons required to keep 2 aircraft over Tripoli when flying from R.A.F. Akrotiri,in any of the above cases.
The lowest requirements,in the case of 12 or 9 hour sorties,can be met only by deploying all 3 Typhoon squadrons to Akrotiri,leaving the United Kingdom with no air defence squadrons.
Human Factors
Flying combat aircraft is a complex task which requires a great deal of mental concentration and physical endurance.
It is difficult for any human pilot to maintain that for extended periods.
Consequently human factors place practical limits on the sortie length which pilots may routinely sustain.
Sorties averaging 3 hours would be considered routine.
Sorties averaging 6 hours would be considered long.
Sorties averaging 9 hours would be considered extreme and beyond what is normally regarded as practical.
Such long sortie lengths have been sustained only by American F15E and F16Cs during the invasion of Afghanistan in 2001.
Sorties averaging 12 hours have never been sustained by any fast jet force in any conflict.
Such long sorties would not ordinarily be considered practical.
It is likely that human factors would rule out the option of fighter sorties averaging 12 hours when planning for a No Fly Zone over Libya.
Tanker Aircraft Requirements
Above we have given the requirements for aerial fuel transfer to keep 2 Akrotiri based Typhoons over Tripoli as follows:
When flying 6 hour sorties 432 tonnes a day will be required.
When flying 9 hour sorties 216 tonnes a day will be required.
When flying 12 hour sorties 189 tonnes a day will be required.
Translating these figures into a requirement for aircraft is far from simple.
Professionals have computer software to help them with that.
One of the biggest issues is that of where and when the fuel must be transferred.
Fighters might need the fuel near their station or they might need to be refuelled on the way to their operating area.
Often the tanker aircraft will maintain a tanker orbit some distance away from the operational area.
There are a lot of ways to do things and that makes it very difficult to come up with an estimate for aircraft numbers.
The tanker aircraft most likely to be used by the Royal Air Force is the VC10.
The Royal Air Force also has a small fleet of larger Tristars but these are extensively used to support operations in Afghanistan.
There are a number of variants of VC10 in service which differ in the amount of fuel they can carry but all can lift at least 77 tonnes of fuel.
As with the fighters,fuel burn varies throughout the flight.
After take off the aircraft is very heavy and is effectively flying up hill requiring a lot of lift and thrust.
When flying home the aircraft is lighter and burns less fuel.
Average fuel burn for a VC10 is about 7 tonnes per hour.
As well as transiting from Akrotiri to Tripoli,a tanker aircraft has to spend time on station waiting to meet up with fighters and then transferring fuel.
This time period can vary considerably depending on circumstances.
If the VC10 spent 5 hours in transit between Akrotiri and Tripoli and 1 hour on station it would burn about 42 tonnes of it's fuel load and have at least 35 tonnes of fuel left for transfer.
In practice they often spend more time than that on station and much of that spare 35 tonnes will be burnt by the tanker aircraft it's self*.
When operating at much shorter ranges during the invasion of Iraq in 2003 Royal Air Force tankers averaged 23.9 tonnes of fuel transfer per sortie.
With so many variables to consider,for the sake of discussion the best we can do is to take that average 24 tonne fuel transfer per sortie from Operation Telic in 2003 and call it a "VC10 sortie equivalent".
That gives us the following estimates for tanker support to keep 2 Akrotiri based Typhoons over Tripoli:
*This highlights the importance of tanker aircraft having refuelling probes.
Fighters will often leave the tanker with plenty of spare fuel,it must then stay on station burning fuel up and waiting until the fighters need more of it or return to base with unused fuel.
Both of these options are inefficient.
But if the tanker aircraft have probes it can transfer that fuel to top up the tanks of an outbound tanker and head for home leaving more fuel for transfer on station.
Unfortunately the Royal Air Force's new A330 tankers will not have the means to transfer fuel to each other in flight which significantly reduces their flexibility.
Air Base Capacity
Having air bases available within a suitable radius of the operational area is only part of the problem.
These bases must also have sufficient capacity to accommodate and support all the required aircraft.
Historically this has consistently been a problem.
The world is not full of spare air base capacity waiting for hundreds of combat aircraft to turn up at short notice.
In practice some aircraft may find bases close to the operational area.
Many others will be at more distant bases.
This increase in distance dictates an increase in the required number of combat aircraft and tanker aircraft.
These in turn require more basing capacity which can only be found at ever more distant locations.
This vicious circle results in a spider's web of dozens of bases spread over entire continents.
The greater the number of aircraft which the task requires,the greater the basing problem becomes.
With most European countries being opposed to a no fly zone over Libya this spider's web of bases may not be available.
The only practical alternative may be American aircraft carriers.
PICTURE BY SSGT DERRICK C. GOODE, USAF
Other Land Basing Options
Bases closer than Akrotiri may make it more practical to enforce a no fly zone over Libya.
Such bases may be available in Greece,Italy and Malta,such as at Sigonella in Sicily.
However,all of those countries are currently opposed to the enforcement of a no fly zone over Libya.
Air Base Defence
Libya has little chance of attacking the British base at Akrotiri on Cyprus due to the large distance.
It does have the ability to attack nearer bases on Crete,Sicily or Malta.
These bases will have to be defended.
Libyan combat aircraft are not formidable opponents.
A single Rapier battery at each air base is likely to be adequate defence.
The United Kingdom has only 4 Rapier Batteries,1 of these is stationed in the Falkland Islands.
Sea Basing Option
Aircraft carriers can be based very close to the Libyan shore.
This results in them spending very little time in militarily useless transit and burning most of their fuel while doing something useful over Libya.
This allows the aircraft carrier to deliver more air power with fewer aircraft at a lower cost.
Illustrious Option
The small British Invincible class aircraft carriers are capable of carrying 2 squadrons of Harriers,each with 9 aircraft for a total of 18 Harrier G.R.9s.
Again rounding numbers up for the sake of clarity and simplicity,we will use the following basic figures for the Harrier's performance.
Endurance of 3 hours at a speed of 500 miles per hour with a fuel load of 6 tonnes and a fuel consumption of 2 tonnes per hour.
A Harrier expert might wish to go into this in more detail.
British aircraft carriers have in the past launched air strikes from as close as 60 miles from a hostile coast for example during the Suez crisis in 1956.
Libyan forces pose little threat to a modern Royal Navy task group armed with the latest version of the Sea Dart,Sea Wolf and Sea Viper missile systems and supported by Seaking airborne early warning aircraft.
There is no reason why Her Majesty's Ships Ark Royal and Illustrious could not have operated 60 miles from Tripoli today.
At this range a Harrier would have about 2 hours and 45 minutes endurance over Libya with no aerial refuelling on a 3 hour sortie.
We have mentioned elsewhere that aircraft carriers generally generate far higher sortie rates than the Royal Air Force manages from land bases.
The Invincible class carriers are known to generate 20 to 25 sorties per day.
During the Falklands War Royal Navy Sea Harriers averaged over 1.4 sorties per aircraft per day of less than 2 hours endurance.
Herein we will work on the conservative assumption of 1.2 sorties per aircraft per day when flying sorties of 3 hours endurance.
We shall also assume 1 sortie per aircraft per day when flying sorties of 6 hours endurance.
A fleet of 18 Harriers could generate 59.4 flight hours over Libya in a day when flying 3 hour sorties with no aerial refuelling.
That is an average of just under 2.5 Harriers kept in the air over Libya around the clock.
H.M.S Illustrious could keep 2 Harriers flying over Libya for 24 hours a day with just 18 Harriers and no aerial refuelling.
Sortie duration could be extended to 6 hours with 6 tonnes of aerial fuel transfer giving 5 hours and 45 minutes over Libya on each sortie.
H.M.S Illustrious could keep 4 Harriers flying over Libya for 24 hours a day with just 18 Harriers and 108 tonnes of aerial refuelling.
H.M.S.Illustrious could also maintain around the clock Airborne Early Warning (E.A.W.) coverage with her Seaking A.S.a.C. helicopters with no aerial refuelling.
As the cost of maintaining a fleet of air refuelling tankers is many times greater than the cost of maintaining aircraft carriers,there are significant financial savings to be had by delivering air power from the deck of a ship.
It was suggested by this blog that retaining 2 or 3 Harrier squadrons instead of a similar number of Tornado squadrons would be both cheaper and more militarily useful.
In addition to retaining the United Kingdom's ability to act independently and in the national interest.
An ability which Britain has now lost.
Harrier G.R.9as could have been cheaply upgraded into multirole aircraft with the installation of surplus Sea Harrier Blue Vixen radars.
This would create a true multirole aircraft capable of dealing with most potential opponents until the F35 arrives in 2020.
Italy,Spain and the United States all operate the similarly upgraded Harrier II Plus.
Bombing Option
It is clear that without aircraft carriers the United Kingdom is capable of providing only a peripheral contribution to any no fly zone over Libya.
An alternative is to use bombing raids to destroy the Libyan air assets on the ground rather than a continuous air patrol.
This is likely to require fewer aircraft and less tanker support than sustaining a persistent presence from Akrotiri.
However,bombing Libya would be a significant military escalation with major political implications.
Bombing is in any case likely to be required to suppress Libyan air defences.
But bombers will require protection from Libyan fighters at least until Libyan fighters have been neutralised.
There will then be a requirement for fighter cover during bombing missions.
Fighter protection may also be required for reconnaissance missions to locate Libyan aircraft on the ground.
Both fighters and ground attack aircraft will have to be in Libyan airspace at the same time.
This will be particularly taxing for the tanker fleet.
Particularly as bombed up aircraft have significantly shorter range than aircraft equipped for air combat.
Nimrod
Long range over water operations by fighter aircraft are often supported by maritime patrol aircraft.
These provide search and rescue cover in case the pilot has to ditch in the sea as well as assisting aerial refuelling operations.
The United Kingdom no longer has such aircraft in service following the scrapping of the brand new Nimrod M.R.A.4 fleet.
The Royal Air Force is likely to require another country to provide such support.
The extreme endurance of the latest Nimrod would also have provided surveillance,close air support and communications capabilities in support of operations over Libya.
Nimrod was capable of operating over Libya from Akrotiri with no aerial refuelling thanks to it's 15 hour endurance.
The 2 remaining Nimrod R1 intelligence gathering aircraft were due to retire imminently but have had a 90 day stay of execution due to the Libyan situation.
Sentry
The distance from Akrotiri to Tripoli is similar to that which Royal Air Force Sentrys opereated at during the invasion of Afghanistan in 2001 when they were based at Thumrait in Oman.
In that conflict they flew 12 hour sorties to generate 8 hours on station over Afghanistan.
To do this required 3 Sentry crews and 2 aircraft to fly a single daily sortie.
Each sortie required about 60,000 pounds of aerial refuelling.
To maintain a 24 hour a day orbit over Tripoli from Akrotiri is likely to require 9 crews and 6 aircraft.
It is also likely to require 180,000 pounds of aerial refuelling per day.
In January 2011 the Royal Air Force had an "in service" fleet of 6 Sentrys,only 4 of those were in the front line "forward fleet" and just 3 of those were available for tasking.
That is not enough to provide round the clock coverage over Tripoli when flying from Cyprus.
Conclusions
Sorties of 9 hours endurance require the smallest number of Typhoons to sustain 2 aircraft over Tripoli for 24 hours a day when flying from Akrotiri.
Such sorties require less aerial refuelling support than other options with the exception of 12 hour sorties.
Although considered extreme,sorties averaging 9 hours have been performed successfully in combat by the United States Air Force,unlike 12 hour sorties which are likely to be considered impractical.
It is unlikely that enough Typhoons will be available to maintain 2 aircraft over Tripoli for 24 hours a day.
It is likely that a single Typhoon squadron with 12 aircraft will be available and will be able to maintain 2 Typhoons over Tripoli for at least 8 hours a day.
If the Typhoons could be based closer to Tripoli they would generate more time on station.
The Sentry fleet could also maintain 8 hours a day of coverage over Tripoli when operating from Akrotiri but would not be able to provide 24 hour a day coverage at that distance.
The aerial refuelling requirements for Typhoons and Sentrys operating over Tripoli from Akrotiri would far exceed available capacity if they were to maintain 24 hour coverage but there would be enough tanker aircraft to provide 8 hours a day of Sentry and Typhoon coverage.
Covering the Eastern parts of Libya from Akrotiri would be more practical than covering the area around Tripoli.
If Italy and Greece allow British aircraft to operate from their bases the resource requirement will decline significantly.
The Invincible class aircraft carriers could have provided a 24 hour combat air patrol and 24 hour a day radar coverage over Tripoli with no aerial refuelling at all with just 18 Harriers and 3 Seaking helicopters.
This is by far the cheapest way to enforce a no fly zone over Libya.
Unfortunately David Cameron has recently ordered that Britain's aircraft carrier capability be retired.
From now on the United Kingdom will be reliant on foreign Host Nation Support to deliver less air power at greater cost to the taxpayer.
David Cameron's decision has eliminated the independence of Britain's foreign policy.
Sortie Rates
The number of aircraft required to generate these sorties depends on a number of factors.
Longer sorties require the aircraft to spend more time in the air and on the ground undergoing maintenance between sorties.
Consequently increasing the sortie length results in each aircraft flying fewer sorties each day.
Different aircraft require different amounts of maintenance between sorties and so some aircraft types will be able to generate fewer sorties than others.
Some air arms tend to generate higher sortie rates than others,the Royal Air Force tends to generate far fewer sorties per aircraft per day than either the Fleet Air Arm or foreign air arms.
The following historical examples of recent fast jet operations may give some indication of how many daily sorties the Typhoon fleet might generate:
During the Falklands War in 1982 the Fleet Air Arm's Sea Harriers averaged over 1.4 sorties per aircraft per day each of which was of less than 2 hours endurance;
During the Invasion of Afghanistan in 2001 the United States Navy's F18s averaged about 1.1 sortie per aircraft per day each of which was typically of 4.5 hours endurance and some of which lasted up to 11 hours;
In Afghanistan today,British Tornados average about 0.7 sorties per aircraft per day flying sorties which typically last 3-4 hours;
During the bombing of Kosovo in 1999,the Royal Air Force's Tornados and Harriers averaged about 0.5 sorties per aircraft per day while flying from bases which ranged from 250 miles from central Kosovo to over 900 miles from central Kosovo for the Bruggen based Tornados which often flew sorties of 7 hours endurance;
During the Invasion of Afghanistan in 2001 the United States Air Force's 12 F15Es of the 391st Fighter Squadron flying from Ahmed Al Jaber in Kuwait,1,500 miles from Kabul,averaged about 0.25 sorties per aircraft per day with an average sortie length of 10 hours,some of these sorties lasted over 15 hours,the longest fighter sorties in history.
Based on these and other historic figures we will make the following estimates for the Typhoon fleet:
An average of 0.8 sorties per aircraft per day of 3 hours endurance per sortie;
An average of 0.6 sorties per aircraft per day of 6 hours endurance per sortie;
An average of 0.4 sorties per aircraft per day of 9 hours endurance per sortie;
An average of 0.2 sorties per aircraft per day of 12 hours endurance per sortie.
Aircraft Requirement
By combining these sortie rate estimates with our estimates of how many Typhoon sorties are required to keep an Akrotiri based Typhoon over Tripoli,we get the following estimates for the number of aircraft required in each case.
When flying 3 hour sorties it is not possible to sustain 2 Typhoons on patrol over Tripoli.
When flying 6 hour sorties 80 Typhoons will be required to sustain 2 on patrol over Tripoli.
When flying 9 hour sorties 30 Typhoons will be required to sustain 2 on patrol over Tripoli.
When flying 12 hour sorties 35 Typhoons will be required to sustain 2 on patrol over Tripoli.
Aircraft Available
The Royal Air Force Typhoon fleet consists of 3 frontline squadrons,each of which now appears to have 12 aircraft (the number of aircraft in each Typhoons squadron was at one time expected to be 17).
There is also a flight of 4 Typhoons defending the Falkland Islands.
Typhoons provide North and South Quick Reaction Alert in the United Kingdom.
This requires at least 2 of these 3 squadrons.
This leaves a single frontline Typhoon Squadron of 12 aircraft which may be available for deployment to Akrotiri.
This is not sufficient to provide the number of Typhoons required to keep 2 aircraft over Tripoli when flying from R.A.F. Akrotiri,in any of the above cases.
The lowest requirements,in the case of 12 or 9 hour sorties,can be met only by deploying all 3 Typhoon squadrons to Akrotiri,leaving the United Kingdom with no air defence squadrons.
Human Factors
Flying combat aircraft is a complex task which requires a great deal of mental concentration and physical endurance.
It is difficult for any human pilot to maintain that for extended periods.
Consequently human factors place practical limits on the sortie length which pilots may routinely sustain.
Sorties averaging 3 hours would be considered routine.
Sorties averaging 6 hours would be considered long.
Sorties averaging 9 hours would be considered extreme and beyond what is normally regarded as practical.
Such long sortie lengths have been sustained only by American F15E and F16Cs during the invasion of Afghanistan in 2001.
Sorties averaging 12 hours have never been sustained by any fast jet force in any conflict.
Such long sorties would not ordinarily be considered practical.
It is likely that human factors would rule out the option of fighter sorties averaging 12 hours when planning for a No Fly Zone over Libya.
Tanker Aircraft Requirements
Above we have given the requirements for aerial fuel transfer to keep 2 Akrotiri based Typhoons over Tripoli as follows:
When flying 6 hour sorties 432 tonnes a day will be required.
When flying 9 hour sorties 216 tonnes a day will be required.
When flying 12 hour sorties 189 tonnes a day will be required.
Translating these figures into a requirement for aircraft is far from simple.
Professionals have computer software to help them with that.
One of the biggest issues is that of where and when the fuel must be transferred.
Fighters might need the fuel near their station or they might need to be refuelled on the way to their operating area.
Often the tanker aircraft will maintain a tanker orbit some distance away from the operational area.
There are a lot of ways to do things and that makes it very difficult to come up with an estimate for aircraft numbers.
The tanker aircraft most likely to be used by the Royal Air Force is the VC10.
The Royal Air Force also has a small fleet of larger Tristars but these are extensively used to support operations in Afghanistan.
There are a number of variants of VC10 in service which differ in the amount of fuel they can carry but all can lift at least 77 tonnes of fuel.
As with the fighters,fuel burn varies throughout the flight.
After take off the aircraft is very heavy and is effectively flying up hill requiring a lot of lift and thrust.
When flying home the aircraft is lighter and burns less fuel.
Average fuel burn for a VC10 is about 7 tonnes per hour.
As well as transiting from Akrotiri to Tripoli,a tanker aircraft has to spend time on station waiting to meet up with fighters and then transferring fuel.
This time period can vary considerably depending on circumstances.
If the VC10 spent 5 hours in transit between Akrotiri and Tripoli and 1 hour on station it would burn about 42 tonnes of it's fuel load and have at least 35 tonnes of fuel left for transfer.
In practice they often spend more time than that on station and much of that spare 35 tonnes will be burnt by the tanker aircraft it's self*.
When operating at much shorter ranges during the invasion of Iraq in 2003 Royal Air Force tankers averaged 23.9 tonnes of fuel transfer per sortie.
With so many variables to consider,for the sake of discussion the best we can do is to take that average 24 tonne fuel transfer per sortie from Operation Telic in 2003 and call it a "VC10 sortie equivalent".
That gives us the following estimates for tanker support to keep 2 Akrotiri based Typhoons over Tripoli:
When flying 6 hour sorties 18 VC10 sortie equivalents
a day will be required;
When flying 9 hour sorties 9 VC10 sortie equivalents
a day will be required;
When flying 12 hour sorties 8 VC10 sortie equivalents
a day will be required.
Royal Air Force air refuelling tanker aircraft consistently generate high sortie rates.
They often fly twice as many sorties per day as Royal Air Force combat aircraft manage.
The tankers often generate an average of around 1 sortie per aircraft per day.
The last time Royal Air Force combat aircraft averaged above 1 sortie per aircraft per day in a major combat operation was in 1956.
As the tankers generally manage about 1 sortie per aircraft per day these "VC10 sortie equivalents" would in effect give us the required number of VC10s.
Thus,depending on the fighter's sortie length we would require 8,9 or 18 VC10s to keep just 2 Typhoons over Tripoli for 24 hours.
In addition,if E3 Sentry's were operationg over Libya from Akrotiri,they would also require refuelling.
This would probably require another 4 VC10s if 24 hour Airborne Early Warning coverage was required over Libya.
Added to the fighter's tanker demands we would need 12 - 22 VC10s in total.
Unfortunately the entire VC10 fleet is only 13 aircraft.
Only about 7 of these would usually be available for operations.
That is not enough to support a round the clock combat air patrol over Tripoli from Akrotiri.
That is not enough to support a round the clock combat air patrol over Tripoli from Akrotiri.
*This highlights the importance of tanker aircraft having refuelling probes.
Fighters will often leave the tanker with plenty of spare fuel,it must then stay on station burning fuel up and waiting until the fighters need more of it or return to base with unused fuel.
Both of these options are inefficient.
But if the tanker aircraft have probes it can transfer that fuel to top up the tanks of an outbound tanker and head for home leaving more fuel for transfer on station.
Unfortunately the Royal Air Force's new A330 tankers will not have the means to transfer fuel to each other in flight which significantly reduces their flexibility.
Air Base Capacity
Having air bases available within a suitable radius of the operational area is only part of the problem.
These bases must also have sufficient capacity to accommodate and support all the required aircraft.
Historically this has consistently been a problem.
The world is not full of spare air base capacity waiting for hundreds of combat aircraft to turn up at short notice.
In practice some aircraft may find bases close to the operational area.
Many others will be at more distant bases.
This increase in distance dictates an increase in the required number of combat aircraft and tanker aircraft.
These in turn require more basing capacity which can only be found at ever more distant locations.
This vicious circle results in a spider's web of dozens of bases spread over entire continents.
The greater the number of aircraft which the task requires,the greater the basing problem becomes.
With most European countries being opposed to a no fly zone over Libya this spider's web of bases may not be available.
The only practical alternative may be American aircraft carriers.
Other Land Basing Options
Bases closer than Akrotiri may make it more practical to enforce a no fly zone over Libya.
Such bases may be available in Greece,Italy and Malta,such as at Sigonella in Sicily.
However,all of those countries are currently opposed to the enforcement of a no fly zone over Libya.
Air Base Defence
Libya has little chance of attacking the British base at Akrotiri on Cyprus due to the large distance.
It does have the ability to attack nearer bases on Crete,Sicily or Malta.
These bases will have to be defended.
Libyan combat aircraft are not formidable opponents.
A single Rapier battery at each air base is likely to be adequate defence.
The United Kingdom has only 4 Rapier Batteries,1 of these is stationed in the Falkland Islands.
Sea Basing Option
Aircraft carriers can be based very close to the Libyan shore.
This results in them spending very little time in militarily useless transit and burning most of their fuel while doing something useful over Libya.
This allows the aircraft carrier to deliver more air power with fewer aircraft at a lower cost.
Illustrious Option
The small British Invincible class aircraft carriers are capable of carrying 2 squadrons of Harriers,each with 9 aircraft for a total of 18 Harrier G.R.9s.
Again rounding numbers up for the sake of clarity and simplicity,we will use the following basic figures for the Harrier's performance.
Endurance of 3 hours at a speed of 500 miles per hour with a fuel load of 6 tonnes and a fuel consumption of 2 tonnes per hour.
A Harrier expert might wish to go into this in more detail.
British aircraft carriers have in the past launched air strikes from as close as 60 miles from a hostile coast for example during the Suez crisis in 1956.
Libyan forces pose little threat to a modern Royal Navy task group armed with the latest version of the Sea Dart,Sea Wolf and Sea Viper missile systems and supported by Seaking airborne early warning aircraft.
There is no reason why Her Majesty's Ships Ark Royal and Illustrious could not have operated 60 miles from Tripoli today.
At this range a Harrier would have about 2 hours and 45 minutes endurance over Libya with no aerial refuelling on a 3 hour sortie.
We have mentioned elsewhere that aircraft carriers generally generate far higher sortie rates than the Royal Air Force manages from land bases.
The Invincible class carriers are known to generate 20 to 25 sorties per day.
During the Falklands War Royal Navy Sea Harriers averaged over 1.4 sorties per aircraft per day of less than 2 hours endurance.
Herein we will work on the conservative assumption of 1.2 sorties per aircraft per day when flying sorties of 3 hours endurance.
We shall also assume 1 sortie per aircraft per day when flying sorties of 6 hours endurance.
A fleet of 18 Harriers could generate 59.4 flight hours over Libya in a day when flying 3 hour sorties with no aerial refuelling.
That is an average of just under 2.5 Harriers kept in the air over Libya around the clock.
H.M.S Illustrious could keep 2 Harriers flying over Libya for 24 hours a day with just 18 Harriers and no aerial refuelling.
Sortie duration could be extended to 6 hours with 6 tonnes of aerial fuel transfer giving 5 hours and 45 minutes over Libya on each sortie.
H.M.S Illustrious could keep 4 Harriers flying over Libya for 24 hours a day with just 18 Harriers and 108 tonnes of aerial refuelling.
H.M.S.Illustrious could also maintain around the clock Airborne Early Warning (E.A.W.) coverage with her Seaking A.S.a.C. helicopters with no aerial refuelling.
As the cost of maintaining a fleet of air refuelling tankers is many times greater than the cost of maintaining aircraft carriers,there are significant financial savings to be had by delivering air power from the deck of a ship.
It was suggested by this blog that retaining 2 or 3 Harrier squadrons instead of a similar number of Tornado squadrons would be both cheaper and more militarily useful.
In addition to retaining the United Kingdom's ability to act independently and in the national interest.
An ability which Britain has now lost.
Harrier G.R.9as could have been cheaply upgraded into multirole aircraft with the installation of surplus Sea Harrier Blue Vixen radars.
This would create a true multirole aircraft capable of dealing with most potential opponents until the F35 arrives in 2020.
Italy,Spain and the United States all operate the similarly upgraded Harrier II Plus.
Bombing Option
It is clear that without aircraft carriers the United Kingdom is capable of providing only a peripheral contribution to any no fly zone over Libya.
An alternative is to use bombing raids to destroy the Libyan air assets on the ground rather than a continuous air patrol.
This is likely to require fewer aircraft and less tanker support than sustaining a persistent presence from Akrotiri.
However,bombing Libya would be a significant military escalation with major political implications.
Bombing is in any case likely to be required to suppress Libyan air defences.
But bombers will require protection from Libyan fighters at least until Libyan fighters have been neutralised.
There will then be a requirement for fighter cover during bombing missions.
Fighter protection may also be required for reconnaissance missions to locate Libyan aircraft on the ground.
Both fighters and ground attack aircraft will have to be in Libyan airspace at the same time.
This will be particularly taxing for the tanker fleet.
Particularly as bombed up aircraft have significantly shorter range than aircraft equipped for air combat.
Nimrod
Long range over water operations by fighter aircraft are often supported by maritime patrol aircraft.
These provide search and rescue cover in case the pilot has to ditch in the sea as well as assisting aerial refuelling operations.
The United Kingdom no longer has such aircraft in service following the scrapping of the brand new Nimrod M.R.A.4 fleet.
The Royal Air Force is likely to require another country to provide such support.
The extreme endurance of the latest Nimrod would also have provided surveillance,close air support and communications capabilities in support of operations over Libya.
Nimrod was capable of operating over Libya from Akrotiri with no aerial refuelling thanks to it's 15 hour endurance.
The 2 remaining Nimrod R1 intelligence gathering aircraft were due to retire imminently but have had a 90 day stay of execution due to the Libyan situation.
Sentry
The distance from Akrotiri to Tripoli is similar to that which Royal Air Force Sentrys opereated at during the invasion of Afghanistan in 2001 when they were based at Thumrait in Oman.
In that conflict they flew 12 hour sorties to generate 8 hours on station over Afghanistan.
To do this required 3 Sentry crews and 2 aircraft to fly a single daily sortie.
Each sortie required about 60,000 pounds of aerial refuelling.
To maintain a 24 hour a day orbit over Tripoli from Akrotiri is likely to require 9 crews and 6 aircraft.
It is also likely to require 180,000 pounds of aerial refuelling per day.
In January 2011 the Royal Air Force had an "in service" fleet of 6 Sentrys,only 4 of those were in the front line "forward fleet" and just 3 of those were available for tasking.
That is not enough to provide round the clock coverage over Tripoli when flying from Cyprus.
Conclusions
Sorties of 9 hours endurance require the smallest number of Typhoons to sustain 2 aircraft over Tripoli for 24 hours a day when flying from Akrotiri.
Such sorties require less aerial refuelling support than other options with the exception of 12 hour sorties.
Although considered extreme,sorties averaging 9 hours have been performed successfully in combat by the United States Air Force,unlike 12 hour sorties which are likely to be considered impractical.
It is unlikely that enough Typhoons will be available to maintain 2 aircraft over Tripoli for 24 hours a day.
It is likely that a single Typhoon squadron with 12 aircraft will be available and will be able to maintain 2 Typhoons over Tripoli for at least 8 hours a day.
If the Typhoons could be based closer to Tripoli they would generate more time on station.
The Sentry fleet could also maintain 8 hours a day of coverage over Tripoli when operating from Akrotiri but would not be able to provide 24 hour a day coverage at that distance.
The aerial refuelling requirements for Typhoons and Sentrys operating over Tripoli from Akrotiri would far exceed available capacity if they were to maintain 24 hour coverage but there would be enough tanker aircraft to provide 8 hours a day of Sentry and Typhoon coverage.
Covering the Eastern parts of Libya from Akrotiri would be more practical than covering the area around Tripoli.
If Italy and Greece allow British aircraft to operate from their bases the resource requirement will decline significantly.
The Invincible class aircraft carriers could have provided a 24 hour combat air patrol and 24 hour a day radar coverage over Tripoli with no aerial refuelling at all with just 18 Harriers and 3 Seaking helicopters.
This is by far the cheapest way to enforce a no fly zone over Libya.
Unfortunately David Cameron has recently ordered that Britain's aircraft carrier capability be retired.
From now on the United Kingdom will be reliant on foreign Host Nation Support to deliver less air power at greater cost to the taxpayer.
David Cameron's decision has eliminated the independence of Britain's foreign policy.
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