AIUI, the purpose of an interceptor is simple, just scramble and get airborne as quickly as possible.
Wonder how well a VTOL jet like the F-35B would do as an interceptor - since it can just rise vertically (if it has a light load,) would that shave 1-2 minutes off of the time used for taxiing and runway takeoff for.a conventional jet like the Eagle?
(Unless it has to go STOVL instead of VTOL)
Wait, the F35 can do VTOL (or something like it)? I was at an air show yesterday where they were showing off all of its capabilities, and they didn’t mention or show that.
But to the question, most of the time in taking off isn’t taken up by jetting down the runway itself, and even if you got off the ground instantly, you’d still need to spend the same amount of time getting up to the same speed (possibly more, if you’re vectoring some thrust down instead of behind you).
In times where a very fast interceptor is needed, I very much doubt that VTOL would help at all. Unless you are in conditions where you don’t have a regular runway. Unless the pilot is in the seat, and the plane is warmed up and ready to go. Then I suppose, you could cut a few miles off the trip to intercept.
Not a pilot, and never been in the military, but I would trade a few thousand (20?) pounds of VTOL ability weight for a faster plane any day.
Well, scrambling a VTOL aircraft to intercept another plane would almost always require accelerating the scrambled plane up to its maximum speed. Since you’re going to accelerate anyway, why not Use your takeoff roll as part of that? I’d be shocked if a scrambled plane’s time-to-altitude was faster with a vertical takeoff than with a rolling one.
If you had many planes and a single runway (like on a carrier) you might get more planes in the air faster if some of them don’t use the runway to take off, but that’s not quite what you asked.
Also, IIRC, vertical takeoffs use a lot more fuel than rolling takeoffs. If a rolling take off is at least as fast while consuming less fuel, why limit your fighting time by wasting fuel on a vertical takeoff?
To be clear, I’m no Marine pilot—or a pilot of any sort.
The F-35 A (USAF) and C (naval version with tail hook) take off and land horizontally, but the F-35 B is a VTOL version for the USMC. It replaces the Harrier.
The B variant carries significantly less fuel than either the A or C variants, which is why I mentioned he fuel required for VTOL takeoffs in my earlier post.
There are three variants of the F-35. F-35A is the Air Force version and is designed for conventional runways. The F-35C is the Navy version and is designed for carrier takeoffs and landings. The F-35B is the Marines version, and this is the one with thrust vectoring capabilities. AFAIK, it’s STOVL. That is it can land vertically, but it still needs a short run for takeoff.
The one you saw at the air show was probably an “A” or “C” variant then. The easiest way to tell those apart is the “A” version has an internal gun in a bulge over the left air intake, while the “C” version has larger wings.
As your cite says, the B is a short takeoff and vertical landing aircraft, not a vertical takeoff and landing aircraft.
I missed the edit window, but Jet Jaguar is correct: the F-35B is STOVL and not (as my post suggests) VTOL.
On a related note, if you’re scrambling fighters in response to other aircraft, your first choice would probably be an F-22. Those are the US’ front-line air superiority fighter and significantly more capable interceptors than any F-35, especially the B variant.
But I’d imagine that in the real world, one scrambles the fighters one has at the time.
ETA: ninja’d on my own correction! 
Generally (at least in peacetime,) the purpose of scrambling interceptors is just to escort some unidentified or adversary aircraft that either doesn’t pose a true threat (the Russian bombers that fly near Alaska and Massachusetts are just saying hi) or would be a piece of cake to shoot down (on 9/11, for instance, any fighter with guns or missiles could have downed the hijacked planes had they been in the right place and time.)
So it wouldn’t need the best fighter you have.
I am currently watching a FOTW series about British pilots training to fly and fight F35s. The take off fast but not vertically but practice landing straight down a lot, even at night in the dark.
You want to intercept where the UFO is going to be by the time you reach altitude. As long as the interceptor has the legs, it wont matter how it launches. When the F-104 was front line they experimented with mounting it on a rocket for a zero/ zero launch, so some thought went into a vtol interceptor.
The F35B is capable of vertical takeoff from a full stop. However, it is classified as STOVL because it has to be almost empty of fuel to take off vertically. It would only do this to reposition the aircraft, since it can only go a short distance.
This confuses people who have seen videos of the F35 taking off vertically. It can do it. But it can’t do it and then go anywhere.
Couldn’t you also use it to take off from an inadequate base, and then refuel in the air (from a tanker plane flown in from a better airbase)?
It’s pretty hard to see modern militaries using inadequate bases today for advanced fighter or strike aircraft. The burden of having weapons, fuel, spare parts, and maintenance equipment on-hand, plus then having to coordinate the jet doing a rendezvous with a tanker – a notoriously big, juicy, defenseless target in any war – would be a much harder thing to pull off than having jets at their expected airbases.
Not to say that it is totally impossible – sure, if there’s a war and things are going weird, air forces may end up doing some unusual things. But for the purposes and scenario described in the OP, tanking a jet takes way longer than taxiing to a runway.
Why not just keep the fighter jet at the better airbase?
Maybe the base the fighter is at was perfectly adequate yesterday, but today there are a bunch of inconvenient craters in the middle of the runway. That sort of thing happens in wars.
You just said the air tankers would be at those better equipped air bases. The tankers getting grounded is no better than the fighters getting grounded.
That’s what the tankers are for, you can refuel/top off fuel tanks while airborne but not arm/rearm the weapons systems. On the aircraft carrier, first to launch was the plane guard/rescue helicopter, then the A-6 tankers, then the weapon-heavy but fuel-light F-14s and A-7/FA-18 bombers. The A-6s would refuel the aircraft after their launch. The order and mix would vary on the mission. For intercepts/escorts, the ready F-14s would go first, followed by the A-6 tankers to meet them partway on the return trip for refueling. I expect the land-based intercepters use the same procedure.
With the destroyers/cruisers in the battle group in anti-air/anti-ship and early warning roles, and our aircraft, I slept very well on the carrier
Refueling isn’t done during or in a battle zone and the tankers are protected by other aircraft and/or anti-aircraft sites/ships.
Craters in the runway can be filled/repaired quickly, that was a lesson learned during WWII.
I was thinking of a situation where one airbase (with F35s stationed at it) is seriously damaged, but there’s another undamaged base within range nearby. But if refuelling isn’t done in combat zones (sensible, I suppose), that probably wouldn’t fly.
Given how laboriously VTOLs slowly take off, I doubt they’re any improvement on conventional designs. I’ve heard that the newer US fighters have thrust exceeding their weight; i.e. you could stand them on their tails and they could climb.