‘Tits Up’ was in common usage in the British Armed Forces, post WW2. It may have originated earlier. The common consensus was that it originated in the Royal Navy. Its use meant ‘complete failure’ (e.g. “the HF radio is tits up”), and was apocryphally ascribed to drowned female bodies floating ‘tits up’ whereas male bodies float face down. I’ve never managed to drown anybody as a yacht skipper, but I’ve tried experiments (with volunteers) in a swimming pool, and relaxed women with at least a C cup tend to float face up, and men face down (the sacrifices I make for science ! 😉 ). The RAF used a euphemism of this – ‘Pear-shaped’ – when socially necessary. Pear-shaped is quoted by the OED to have originated from RAF usage in 1983 (used in the book ‘Air War South Atlantic’), and I was an RAF pilot in 1983, so can confirm this meaning.