OpenRA

A suggestion for the (little used) Radar Jammer-- how about it could also block GPS? And be available to all sides? (I'm assuming it doesn't already block GPS.)

I think the original game made them available to both allies and soviets?

Why do it? Well to have some sort of counter to GPS; although of course the Radar Jammer wouldn't help naval, and wouldn't help in many cases when using helis/planes.

Also, people sometimes complain that Soviet naval is imbalanced as there is no equivalent to destroyers; and radar jammers could help defend Soviets against destroyers, especially if also using teslas.

No, it wasn't available to Soviets in original. And shouldn't be.

Giving it the ability to block GPS is a decent idea, however it doesn't in any case solve the GPS problems even if available for soviets (which it shouldn't be).

Very bad idea, if soviet would have the jammer they could defend destroyers, longbows and chronotanks, wich wold cause a massive imbalance in this game.

Why are people complaining that there is no equivalent to destroyers?
Are they just noobs who doestnt know how to use subs?

Subs are much more deathly against naval !

Subs are good very early game, and they do give some useful vision. However they cost 1000$ I think, can't do any damage to land units or air units, (unlike destroyers), and are really quite easily destroyed by allies air when they surface to fire.