In the early 1950s, the Air Force closely monitored the introduction of surface to air guided missiles (SAM) such as the Nike Ajax into service with the Army Anti-Aircraft Command. Under joint operating doctrine for continental air defense at the time, SAMs were the Army’s responsibility, with fighter interceptors an Air Force role. The Air Force was interested in a very long range SAM system, however, and adopted the quaint stance that such a SAM was simply an unmanned interceptor.
Building on earlier work with GAPA, Boeing was teamed with the Michigan Aerospace Research Center (MARC) to develop a long range pilotless interceptor. Between BOeing and MARC, the project was quickly dubbed BOMARC.
Two major challenges for a long range SAM were propulsion and guidance. Rocketry was still rather primitive, and a rocket motor simply couldn’t provide the range needed. A gas turbine couldn’t provide enough thrust for high speed except at great expense. Boeing instead proposed using the simple Marquardt ramjet to give the missile a speed of about Mach 2.8 and a range of about 200 miles. Ramjets are simple and work very well at high speed, but they cannot provide thrust at zero airspeed, so a booster rocket was needed to accelerate the missile off the launch pad. Solid motors were considered, but a sufficiently powerful one wasn’t available, so a liquid fueled rocket was built into the after end of the airframe.
Even at M2.8, at would take a BOMARC some time to reach its 200 mile range, and so a mid-course guidance was needed to keep the missile on track to intercept. Here is where Boeing and MARC came up with a pretty elegant solution. Air Defense Command was already using the SAGE network to provide steering commands to manned interceptors. BOMARC would simply use that system to provide steering commands to the missile autopilot. Terminal guidance would be an onboard active radar pulse doppler seeker.
The warhead was either a 1000 pound conventional warhead, or a 10 kiloton W40 nuclear warhead.
The missiles would be stored horizontally in semi-protected bunkers nicknamed coffins, and raised to vertical for launch. The liquid fueled rocket had to be fueled immediately before launch, which was both somewhat dangerous, and took a few minutes, which, if a real intercept was at hand, was an obvious drawback.
The Air Force had originally planned 52 launch sites with 120 missiles each. In the event, costs of the system, budget cuts, and developmental problems led to the deployment being scaled back to a handful of sites in the US and Canada, with a total of about 570 operational missiles being built, with maybe another 100 development and service test missiles also built.
Even before the BOMARC was deployed, Boeing and Morton Thiokol worked on developing a sufficiently powerful solid booster. After about 290 “A” model BOMARCs had been delivered, production switched to the “B” model with the XM51 solid booster. As an added bonus, the XM51 took up much less space in the airframe. That extra space was used for more fuel (the ramjet ran on 80 octane gasoline), giving the “B” model more than double the range, over four hundred miles.
With this much improved missile entering service, the earlier A models were soon converted to high speed drone targets.
BOMARC served from 1959 to 1972. As the threat of intercontinental ballistic missiles increased, the BOMARC became increasingly irrelevant, and a costly white elephant. It was the only surface to air missile system the Air Force ever developed.
A bit on designations- BOMARC was, as noted, concieved as a pilotless interceptor, and thus was initially numbered under the fighter designation system as F-99. The Air Force soon changed its designation system for guided missiles and changed the designation to IM-99 (intercept missile). Under the revised 1962 Tri-Service Designation system, the BOMARC became the CIM-10.