The F-35B has been delivered to an American base for testing of its vertical take-off and hover capabilities:
The F-35 “Lightning II” B model will, like other versions of the same aircraft, offer supersonic performance and stealth technology – a combo so far offered in only one aircraft in the world, the famous F-22 Raptor ultrasuperfighter. But the F-35B, unlike its tailhook and normal-runway counterparts, is also equipped with a central lift fan mounted in a shaft through the fuselage and can swivel its jet exhaust downwards too.
This means that an armed and fuelled F-35B should be able to make a very short takeoff run to get airborne and then, having burned fuel and perhaps released weapons, make a vertical landing supported entrirely by engine thrust. This Short Takeoff and Vertical Landing (STOVL) capability has so far been offered in the Western-aligned world only by the famous Harrier, originally developed in Britain and now in service with the RAF, the Royal Navy and the US Marines.
Of course, Britain’s interest is moving toward being purely intellectual . . . the bookies are offering long odds on Britain ever commissioning even one of those two new aircraft carriers, never mind both of them. Back story here, here, and here.