Yeah you heard that right, the US almost used a British ship design which I had made earlier in the week about the Type 24 and 25 Frigates
If you are wondering what that looked like
Side Note: my time management isn’t good and when I’d found information on the ships, I’d want to share cause I was sure no-one had even heard of the ship….but let’s get back to ship
Unlike the British who used the 4.5″/55-calibre Mark 8, the US Navy would use the 5″/42-calibre Mark 42.
For its offensive missile armament, it was to have two 4-cell Mark 141 Quad Launcher for 8 RGM-84 Harpoons probably the RGM-84D Harpoon
The Anti-Air Defense was two 8-cell Mark 29 Guided Missile Launcher System with 16 RIM-7 Sea Sparrow
Like most UK-designed ships, it would have used two twin 30mm cannons likely the 30mm GCM-A03 Twin Oerlikon Autocannons.
Her Aviation Wing was to be two helicopters probably two Kamen SH-2 Seasprites as given the size of the Sikorsky SH-3 Sea King might not allow two onboard, I’d say she was more than likely gonna be equipped with Kamen SH-2 Seasprites.
So why did the USN turn this down? What might have happened had the USA bought the Type 24 frigate? well for one the Constellation Class Guided-Missile Frigate would have been its replacement had it been built.
There are multiple reasons for starters this would have been going up against the Oilver-Hazard Perry Class Design
And as Reddit user Fantastic_1 highlighted
Most sources indicate this was a cheap export or ASW-centric design. Along with the Type 25, these exercises in design eventually rolled into the Type 23. Given the sparse details, it is really doubtful the Type 24 was actually offered to the US.
No business case for the US as a customer. At the time, the US had a massive shipbuilding capacity, with several combatant designs in production or beginning production in the 70s.
diamondsofthenight 
