The Lockheed Martin F-35 Lightning II is being produced in three variants: A
conventional land based version for the USAF designated the model "A", pictured first below,
a STOVL (short take-off vertical landing) version for the USMC, the Royal Air Force and the Royal Navy designated the model
"B", shown in the video, and a carrier-based version for the U. S. Navy designated the model "C" pictured second below.
In the model "B" STOVL, the weight and size of the lift fan in the aircraft takes up room that would normally be used to carry weapons and fuel.
If you examine the video closely, you can see the opening for the air intake of the lift fan directly behind the cockpit.
The F-35 model "C" is a version of the basic aircraft with modifications to adapt it to
aircraft carrier operations. It is intended to be the U.S. Navy's first