you are indeed correct, phonesis. tactical ops - "to" to its fans - did start off as a ut mod.
i got into it during its early mod phases. was at its peak in version 2 - 2.2 iirc. i remember when it went retail and the game completely changed. a victim of commericalisation. the gameplay and graphics completely changed. it didn't feel like the fun mod i knew and loved, it felt like a game that was slapped together in a rush to meet deadlines.
the gameplay was drastically re-done via patches after the game went retail too.
all in all, a once great game with a once great and tight-nit community. all but dead now. their forums are still reletively active by the hardcore members of the community.
to be honest, counterstrike was better. in every single way.