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SAMPLE TEXT FROM A WARHEAD HISTORY:
MK 41
In late June 1955, the DOD requested a feasibility study of a new Class "B" gravity bomb and ICBM warhead. The Air Force's Strategic Air Command had come up with a requirement for a new 10,000 lb., 62"-diameter weapon. By the summer of 1956, the DOD also had a requirement for a 60" diameter, 10 MT, 10,000 lb. Class "B" bomb and warhead. (1)
To satisfy these requirements, UCRL proposed the use of an existing thermonuclear device, the three-stage BASSOON, which could easily be "weaponized." The device might be the forerunner of both new Class "B" (20,000 lbs.) and Class "A" (30,000 lbs.) high-yield weapons. Although there was little probability that a weaponized version of the latter would be tested, scheduling of the new device for test during REDWING might result in weapons entering stockpile by as much as two years earlier. (2)
The proposed UCRL device was test-fired in "clean" and
"dirty" configurations during the Zuni and Tewa shots of Operation
REDWING in 1956; yields were 3.5 and 5 MT, respectively. The second test version
of the device weighed nearly 3,600 lbs. more than the first. By mid June 1956,
stockpiling of the new Class "B" bomb was to begin in January 1959. (3)
Three months later, the development of the new Class "B" weapon was partially dependent upon a test shot then planned for Operation HARDTACK in the spring of 1958, a year and half hence. This development was still aimed at a 10,000 lb. total weight bomb, and although the yield attainable in this weight would not be known definitely until after HARDTACK, it was likely that a 10 MT yield could be achieved.
Both LASL and UCRL planned to study for about the next four to six months the optimum design for weapons in this size range. Among the specific factors to be studied would be both two- and three-stage thermonuclear systems, and possible characteristics of a "clean" version.
Thus it appeared that the establishment of firm military requirements, including guidance on whether a conventional or "clean" version was desired, would not be necessary until January 1957. An operational availability date of February 1959 was set for the bomb. (4)
The feasibility report requested by DOD in June 1955 was completed in
November 1956. The UCRL proposal was accepted and the nomenclature TX/XW-41 was
assigned to the weaponized device. At a meeting in December, the AEC revealed
plans to conduct the first drop tests of the bomb version from a B-47.
On January 28, 1957, the DOD requested the AEC to develop a new Class "B" weapon using the UCRL design. The military characteristics for the bomb and warhead were approved by the MLC in mid-February, and development engineering of the designs began . (5)
At this time, the TX-41 was expected to weigh 10,000 lbs. and be 54.5" in diameter. Potential delivery vehicles included the B-58 "Hustler" bomb/fuel pod. In addition, the XW-41 warhead had been authorized for development in November 1956 for application to the NAVAHO surface-to-surface missile. (6)
By mid-March 1957, the MLC was requesting the AEC to place equal Phase 3
development effort on both the clean and conventional versions of the new Class
B weapon.
At the same time, DOD noted that while the AEC had already spent time and money on development effort of another weapon for which DOD never established a requirement, that device was undesirably heavy, and its yield loss when converted from conventional to "clean" configuration was totally unacceptable. In light of these factors, and because the new Class B weapon would be available relatively soon, the DOD recommended that the AEC discontinue its development of the device. (7)
The DMA requested parallel development of a "FUFO" full-fuzing option MK 41 weapon in early April. FUFO allowed five fuzing options: free-fall airburst; parachute-retarded airburst; free-fall surface burst; parachute-retarded surface burst; and "laydown," parachute-retarded delayed surface burst.
The proposed ordnance characteristics of the TX-41 bomb and XW-41 warhead were presented to and accepted by the SWDB on June 20. The ICBM warhead application was canceled at the end of July.
Shot Smoky, a test of the boosted TX/XW-41 warhead primary and secondary in a bomb mockup, was fired at the NTS on August 31. The device yielded 44 KT (predicted yield was 48 KT); it measured 50" in diameter and 126.2" in length and weighed 9,408 lbs. The test included some thermonuclear yield. (8)
Drop testing of the TX-41 was conducted between December 1957 and December 1959 at the AEC's Tonopah (Nevada) and Salton Sea (California) test ranges (see Table 4-22). Drop altitudes ranged from 1,500 to 50,00 feet at speeds between 300 and 600 MPH. The 36 tests were successful for the most part. Parachute development for the MK 41 was conducted in parallel with drop testing. Figure VI-88 shows an early MK 41 drop shape in an MHU-23/C "clip in" subassembly consisting of an MHU-13/C support and ADU-18/C adapter set.
Early variants of the TX-41 bomb were fired during the Sycamore, Poplar and Pine shots of Operation HARDTACK Phase I at the PPG between May 31 and July 27, 1958. The Sycamore test used a two-stage "clean" version of the TX-41; predicted yield was five megatons, of which just 200 KT was to be fission yield, but actual total yield was only 92 KT. The Sycamore test device was 50 inches in diameter by 112.6 inches long and weighed 9,723 lbs.
The Poplar shot on July 12 was a repeat test of the "clean" two-stage variant, with diameter reduced to 48.2 inches, length reduced to 112.1 inches, and weight reduced to 9,316 lbs.
The Poplar device was predicted to yield either five or 10 megatons, of which
only 450 KT was to be fission yield. The test device functioned well, with a
yield of 9.3 MT, one of the larger HARDTACK Phase I yields
The Pine shot on July 27 used a "clean" three-stage configuration; of
a predicted total yield of four to six megatons, only 200 KT was to be fission
yield. The dual-primary device had the same exterior dimensions as the Sycamore
device, but with its weight reduced to 8,752 lbs. Total yield was only two
megatons, about one-half to one-third the predicted value.
The ordnance characteristics of the TX-41 were revised and accepted by the SWDB in mid-October 1958. Production engineering of the TX-41 started soon afterwards.
High-speed characteristics of the TX-41 were determined in a 10'-diameter transonic wind tunnel in May 1959; the MK 41 Mod 0 was design-released in September and all flyaround and drop tests of the TX-41 were completed by January 1960.
Studies later in 1960 indicated that the TX-41 might not be suitable for carriage and release by the B-70 because of high bomb bay temperatures resulting from Mach 3 flight. Four schemes were examined to protect the TX-41 from overheating, but not one kept all weapon components within allowable extremes and marriage of the TX-41 to the B-70 was eventually abandoned.
Early production of the MK 41 Mod 0 bomb began in September 1960; by June 1962, approximately 500 units had been manufactured. These weapons were retired between November 1963 and July 1976 as the more-versatile MK 53 replaced them in the stockpile.
The MK 41 was 12' 2" long, 50" in diameter, and weighed 10,670 lbs. Tail fins spanned 74." The bomb carried a 5-foot diameter pilot chute and a 16 1/2-foot diameter ribbon chute for high-speed stabilization. Yield was less than 10 megatons. The warhead, described as a "Class B fin-cone weapon," could be fuzed for air or surface burst.
The MK 41, with a yield of 25 MT, was both the only three-stage weapon to ever be stockpiled by the U.S. and also the highest-yield weapon ever stockpiled.
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