here is a report about Rockwell XFV-12.
According to George Spangenberg, Evaluation Division Director of NAVAIR, the push for the XFV-12 came from NAVMAT. Specifically from Rear Admiral Thomas Davies head of R&D at NAVMAT, who felt that the Navy's frigates and destroyers could not do the ASW mission, and small carriers with ASW helos could get the job done. Naturally, said carriers would need air defense if they were going to operate on their own, AEGIS being nearly a decade away, and in 1972, in an unprecendented move by NAVMAT, feelers were sent out to the aerospace industry for a VTOL long range senor aircraft and a high perfomance VTOL fighter. A wide variety of proposals from the industry came back, and NAVMAT had NAVAIR review them. The submissions were all over the place, ex C-130 variant, because the Sea Control Ship was so poorly defined. As you mentioned before a lot of squids were worried that a supplement such as the SCS would end up being shoehorned in as the main type of carriers due to budgetary concerns.
This was at the time in the OSD that prototyping was all the rage and the Navy would be allowed one prototype. The three final fighter designs considered were the McAir's AV-16, Rockwell's North American Columbus Division's FV-12 and General Dynamic's Convair Division 200. Using the lift+cruise VTOL method, the Convair 200 coming in first place because it could do the air-to-air well and possibly air-to-ground, the Harrier variant AV-16 placed second as it couldn't do the a2a mission being so slow, but had a2g capability and the thrust augmented wing FV-12 dead last since it would not be able to do either role effectively. NAVAIR gave a presentation to NAVMAT recommending that work on a lift engine be started before prototype of a fighter be ordered, and for the sensor aircraft a modified OV-10 with thrust augmentation system could be prototyped at minimal cost. Adm. Davies took the charts from the NAVAIR presentation then modified and cherry picked the data for his FV-12 sales pitch to Assistant Secretary of the Navy Frosch, who gave the green light. With NAR-Columbus promising Mach 2.0 speed and 55% lift augmentation, the project also had support from OpNAV's "high risk, high pay off" officers. The aircraft was chosen a the Navy's aircraft to prototype and funded.
Soon there after NAVAIR's reservations about the design reached Assistant Secretary Frosch, and he blew a gasket. Frosch called in representatives from NAVMAT, CNO, CNM and NAVAIR to talk the project over, stating he never wanted any project to be pitched to him again without both sides of the story being told. The next year, Dr. Frosch left the Navy for the UN Environmental Program and then NASA. Adm. Davies, the instigator of the program, retired from the navy to become Assistant Director of the United States Arms Control and Disarmament Agency which he held for 7 years. Ground testing of the engine began in 1974. NASA wind tunnel studies showed that the vertical lift figures were overly optimistic, yet the program still continued. *insert VTOL sabotage conspiracy theories here* In 1977, 5 years after go ahead, the first (and after the second was cancelled) and only prototype was rolled out, cobbled together from various A-4 and F-4 parts with a still uncertified engine originally meant for the F-14 (F401). In a 6 month period in 1978 during tethered test the XFV-12A was only able to achieve vertical flight under its own power a total of once, earning it the title of "ground hugger-1". The augmented lift wing only deliver 25% vertical thrust, only enough to lift 75% of the airframe's total weight, primarily due to loss of thrust through extensive ducting. It didn't help either that the airframe was overweight.