The Boeing CIM-10 Bomarc was a surface-to-air ramjet powered long-range missile used for the air defence of North America. The BOMARC (“BO” from Boeing and “MARC” from Michigan Aeronautical Research Centre) was the first operational long-range SAM and the only SAM deployed by the United States Air Force. It was originally designated as the XF-99, later changed to IM-99 and then re-designated as the CIM-10A.
The missile was stored horizontally in shelters, with movable roofs and was erected before being fired vertically, using rocket boosters , and having reached the desired altitude, tipped on to a horizontal position. At this stage, the ramjets took over, giving a cruise speed of Mach 2.5 with a range of about 700 kilometres.
The Bomarc A missile used liquid-fuel booster that took two minutes to fuel before launch. This was a serious limitation as it meant loss of valuable time for a high-speed intercepts. Plus, the hypergolic propellants (hydrazine and nitric acid) were very dangerous to handle, leading to several serious accidents.
In the mid-1950s, a new solid-fueled Bomarc variant, the IM-99B Bomarc B was developed that used a Thiokol XM51 booster, and also had improved ramjets. The first IM-99B was launched in May 1959, but problems with the new propulsion system delayed the first fully successful flight until July 1960. With lesser space being taken up vis a vis the liquid propellant, more ramjet fuel could be carried and it increased the range to 700 km.
For guidance, Bomarc relied on the Semi-Automatic Ground Environment (SAGE), an automated control system used by NORAD for detecting, tracking and intercepting enemy bomber aircraft. The missile was guided to the vicinity of its target at which time it came under control of an internal target seeker pulse doppler radar – the first system to have a pulse doppler aviation radar. The terminal guidance allowed it to home on to the target area and as it neared the target, the onboard radar proximity fuse detonated the warhead, either a large conventional explosive or the W40 nuclear warhead.
Testing of prototypes began in 1952 and the -A series was declared operational in 1960 but the first US site was declared operational in 1959, but with only a single working missile.
The Air Force originally planned for a total of 52 sites covering most of the major cities and industrial regions in the US. As testing continued, the Air Force reduced its plans to sixteen sites, and then again to eight with an additional two sites in Canada.
The Bringing the rest of the missiles into service took years, by which time the system was obsolete. Deactivations began in 1969 and by 1972 all Bomarc sites had been shut down. A small number were used as target drones, and only a few remain on display today.