US air and naval combat power immediately available in the region is at relatively low levels. Some of the combat aircraft assembled to prosecute the campaign against the Islamic State, also known as ISIS or ISIL, have already been moved on to other operations. In terms of tactical aviation, only two squadrons remain active over Syria: the 336th Expeditionary Fighter Squadron with F-15E Strike Eagles based at Mowafaq al Salti in Jordan, and a half-strength F-22A Raptor squadron at Al Dhafra in the United Arab Emirates, believed currently to be the 94th Expeditionary Fighter Squadron. The US also still has two Expeditionary Attack Squadrons (46th and 361st) equipped with MQ-9A Reaper UAVs in theatre, based in Jordan and Kuwait, but the utility of these assets and their UK Royal Air Force (RAF) counterparts for the kind of missions being contemplated is limited by the contested nature of the airspace. The bomber detachment at Al Udeid in Qatar is also still in place: the 34th Expeditionary Bomb Squadron’s B-1B Lancers began replacing the previous B-52H Stratofortress rotation at the beginning of April. Additional bombers, particularly the B-2A Spirit stealth bombers, either flying from their home bases in the continental United States, or staging from forward bases such as Diego Garcia in the Indian Ocean, are an obvious way of getting combat power into theatre for an initial strike.
There has been some identifiable movement of additional US tactical aviation assets into Europe and the Middle East since the alleged chemical attack, but it is not clear that they are directly related to any potential Syria operation; they are more likely to be pre-planned rotations for enduring commitments. These include half a dozen Indiana Air National Guard A-10Cs from the 163rd Fighter Squadron and nine Marine Corps F/A-18A+ Hornets from VMFA-115 arrived at Lajes in the Azores after a transatlantic flight, and then departed for the Mediterranean on 11 April.
Both the UK and France also have squadron-sized tactical combat aircraft deployments in the region as part of the campaign against ISIS. The RAF has a mixed force of six Typhoon FGR4s and eight Tornado GR4s deployed to Akrotiri in Cyprus, and the French have six Rafales deployed to Al Dhafra in the UAE under Escadron de Chasse 1/7 Provence and a detachment of four additional Rafales stationed at Prince Hassan airbase in Jordan. The RAF Tornados and the French Rafales are capable of conducting stand-off attacks from outside Syrian airspace using Storm Shadow and Scalp EG cruise missiles, and additional long-range cruise missile missions could be flown direct from France or the UK, as they previously were during operations over Libya in 2011.
At sea, the situation is similar. There is no aircraft-carrier group currently assigned to either the US Navy’s 5th or 6th Fleet. The USS Harry S Truman and Carrier Strike Group 8 departed Norfolk, Virginia, at least five days away from the theatre, on 11 April. Of the four Arleigh Burke-class destroyers carrying Tomahawk cruise missiles, which are forward based with the 6th Fleet, only one, the USS Donald Cook, was in the Eastern Mediterranean on 7 April. Two of the others, USS Ross and USS Porter, were conducting port visits in the UK and France, and the fourth, USS Carney, had recently returned to its homeport of Rota in Spain. Currently deployed alongside the Donald Cook is the French Navy destroyer Aquitaine, equipped with the new Missile De Croisière Naval (MdCN) cruise missile but with a smaller number of total launch cells compared to her US counterparts. The UK Type-45 destroyer HMS Duncan is currently in the Eastern Mediterranean as the flagship of NATO’s Standing Maritime Group 2. Although she is not equipped for land-attack missions, she may still be diverted to the theatre in order to bolster the air-defence capability of any task group (and indeed RAF Akrotiri) against potential reprisals.
Below the waves the picture is somewhat better: the USS John Warner, a Virginia-class Block III submarine, left Gibraltar last week, and after a brief stop at Toulon on 9th April is now highly likely to be in the Eastern Mediterranean. The Ohio-class converted guided-missile submarine USS Florida (capable of accommodating up to 154 Tomahawk cruise missiles) was believed to be in the Indian Ocean in March, but may have subsequently returned through the Suez Canal and re-entered the Mediterranean, and it is possible that additional submarines from the 5th and 6th Fleets have been moved to join them. Although there is at present no official confirmation from the British government, several media reports have suggested that at least one of the Royal Navy’s submarines, able to launch Tomahawk cruise missiles, may also be en route.
In addition to air and naval assets, theoretically the US could also call upon ground-based ATACMS short-range ballistic missiles with a range of up to 300 km, fired from M142 HIMARS launchers based either within Syria itself or in a neighbouring country. However, the vulnerability of these systems and their bases to counter-attack by Syrian, as well as Russian, capabilities will likely lower the attractiveness of this option to military planners.
The presence of Russian and Iranian personnel on the ground in Syria working with government forces, and the advanced capabilities of the deployed Russian systems, will significantly complicate any US and allied planning. The mobile Pantsir-S1 and Buk-M2E air-defence systems, acquired by Syria from Russia, are capable of posing a serious challenge to Western tactical aviation, despite relatively short ranges. The batteries of S-400 and S-300V4 long-range surface-to-air missiles the Russians have deployed to the airbase at Khmeimim and the naval base at Tartus will be even more concerning, and although neither system has seen combat, allied planners will treat both with a healthy respect. The same applies to the combat aircraft Russia maintains at Khmeimim – even if a direct engagement between US and Russian aircraft is unlikely, any ground-attack missions will likely need to be accompanied by a reasonably potent air-to-air support package to guard against the possibility. Likewise, the handful of Russian frigates and submarines thought to be at sea in the eastern Mediterranean could complicate deployment plans for US and allied naval commanders.
With a potentially enduring US and allied presence in parts of southern and eastern Syria still under discussion, there may be significant thought given to attempts to draw a clear distinction between these and any assets used for a strike mission in response to the alleged chemical weapons attack. This, together with the potential air-defence threat, may weigh in favour of simply employing a combination of bombers flying from the continental US and/or Diego Garcia and long-range cruise missiles fired from surface vessels and submarines. But, combined with the lack of operational surprise, this could limit the scope of targets that could be prosecuted.
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