United Kingdom Defence Secretary Philip Hammond announced on 9 May 2012 that both the Royal Air Force and the Royal Navy will now operate only the F-35B short takeoff and vertical landing variant instead of the F-35C carrier variant. Hammond noted several reasons for switching back to the F-35B, including: sticking with the F-35C would delay the planned Carrier Strike effort by three years to 2023; the cost of fitting catapults and arrestor gear to the Queen Elizabeth-class carriers to operate the F-35C had doubled to approximately £2 billion (approximately US$3.1 billion); and operating the STOVL aircraft offers the UK the ability to have continuous carrier availability. Flight trials with the F-35B off the HMS Queen Elizabeth are scheduled to begin in 2018.