I don't usually build any spies, but in my latest game (random leader - got Vicky, Monarch, Pangaea map, random sealevel/climate, normal speed) I screwed up: took out Freddy early on and crippled Caesar, palled up to Mansa Musa and Hatty but let Mao and Tokugawa both get further ahead of me than I could cope with - boxed in by Mao and he was too far ahead militarily. Diplo was out (Mao and Tok loved each other and hated me - they were the two biggest civs) and I was nowhere culturally. So I consolidated the land I had/could take and went into spacerace mode. Which I was clearly losing to Mao by some distance, so as a last ploy of desperation I decided what the heck, build some spies and sabotage Mao's production.
So, one Kremlin and some spies later, I've identified the cities where the expensive bits are being made. The manual says my spies can "destroy production" - however I don't even have this option available (it's non-pressable), all I can do is try to steal plans. When I move the spy to another city (making an aircraft) it does let me "destroy production". But this only seems to destroy the production for one turn. I'd read the manual as meaning that if this succeeded (and it's only marginally over 50% likely to) all the production on that unit would be lost (otherwise why would this be useful at all, let alone "quite devastating when a city is just a couple of turns away from producing a wonder".
Are spies todally useless or am I missing something obvious - very grateful to anyone who can help clue me in
. How come I don't even get the option to "destroy production" in the cities it's going to be useful (the ones that are losing me the game), and how come when I do it doesn't seem to do what it says on the tin?
Many thanks in advance for any help you guys can give!
So, one Kremlin and some spies later, I've identified the cities where the expensive bits are being made. The manual says my spies can "destroy production" - however I don't even have this option available (it's non-pressable), all I can do is try to steal plans. When I move the spy to another city (making an aircraft) it does let me "destroy production". But this only seems to destroy the production for one turn. I'd read the manual as meaning that if this succeeded (and it's only marginally over 50% likely to) all the production on that unit would be lost (otherwise why would this be useful at all, let alone "quite devastating when a city is just a couple of turns away from producing a wonder".
Are spies todally useless or am I missing something obvious - very grateful to anyone who can help clue me in

Many thanks in advance for any help you guys can give!