What If ideas on this theme
I suppose the main question is why would you
want to add missiles to a tank? I can see roughly three rationales for it (note that I don't necessarily agree with any of these personally, but this is how the thinking might go):
1. ATGWs on a Main Battle Tank.The only reason I can see for doing this is to extend the tank's engagement range and maintain lethality out to maximum range. In the period where most of these schemes were proposed ('60s/'70s), heavy ATGWs comfortably out-ranged tank guns and a HEAT warhead is just as lethal whatever speed it's doing, whereas an APFSDS round gets less lethal as it slows down with distance travelled.
This argument is probably most persuasive for the lightly-armoured 1960s "protection-through-speed" MBTs such as the Leo I, AMX-30 and Vickers MBT, since they can least afford a point-blank slugging match with any gun of three-figure calibre, and so they have a vested interest in thinning out the opposition at the greatest possible range. Problems are quantity of reloads, difficulty of reloading and increased fire/explosion hazard.
Whiff ideas:
Pz.61/68 with ATGWs (not sure if there's a kit).
T-55/T-62 with external ATGWs instead of gun-launched ones.
Leo-1/AMX-30 with ATGWs.
2. Light Tanks/Armoured Cars with ATGWs.This is possibly the most useful option, as the AMX-13/SS-11 demonstrates. A vehicle whose primary function is recce/escort/screening may very well come up against enemy MBTs yet it can't possibly carry a tank-killing gun because it's too small and light. Adding ATGWs gives it some "equalisers". Difficulties are all the same as the MBT platform, but less significant since any tank-killing rounds (even a small number) are better than none, and light tanks in combat with MBTs are chronically vunerable anyway.
Whiff ideas:
M41 Walker Bulldog with M47/Vickers MBT style ATGWs (not neccessarily Swingfire). This would be essentially a US version of the AMX-13+SS-11 combo.
M26 Chaffee: as above. Installation probably more like the Saladin/Swingfire setup.
PT-76 with AT-3 Sagger mounted over the gun in similar style to the BMP (this is another one which I find it hard to believe hasn't been tried for real).
3. Retro-fitted oldies.You might imagine a nation with a fleet of WWII leftover tanks which can't, for political or economic reasons, get them replaced or refitted abroad, and doesn't have the heavy engineering design & production capability to up-gun them locally. It is, however, a lot easier to bolt rails/boxes to the outside of a tank than it is to fit it with a new gun, and it's also quite easy to disguise the origin of an illegally copied ATGW with minor changes to fin shape and box style.
Whiff ideas:
Put "local" versions of any early ATGW onto any of the following platforms, chosen for their post-war availability:
M4 Sherman
M3/M5 Stuart
M26 Chaffee
Comet
T-34/76
T-34/85
M8 Greyhound