In response to the person who said that my statement that modern diesel subs were derived from Type XXI was invalid, I have this to say.

The subs I mentioned are far from modern, they are now all second line submarines first commssioned in the late fifties to early sixties. However, al;l have a cigar-shapoe hull form adopted from Typoe XXI, and those boats are second generation derivatives. based off of submarines which were directly copied from tyoe XXI. By this time, however, they had abandoned the figure-eight internal hull configuration.

About Argentina's Type 209s, and tehir lack of success, wouyld be willing to bet it was bad torpedoes. Type 209 has a good fire control suite, but that only does any good with modern torpedoes. I don't reckon the Argentines were using state-of-the-art, like the Mark 48 ADCAP, or Marconi's Tigerfish torpedo. Probably the best they could get their hands on were Mark 37s, an aging american torpedo. But I would bet they were using straight-runners, and probably old ones. If that's the case, tehy could have run cold, run the wrong course, not exploded, exploded prematurely, etc. That's just a guess, but I know that lots of those sort of countries fall short on the weapons end of their submarine forces..