Previous designs Late in
World War II, the German Army began experimenting with modified versions of the
Ruhrstahl X-4 wire-guided missile. Originally developed for the
Luftwaffe as an anti-bomber weapon, by changing the warhead to one using a
high-explosive anti-tank (HEAT) design, the new X-7 version made an effective anti-armor weapon with a range of hundreds of meters. This would greatly improve the effectiveness of infantry anti-tank operations, which at that time were generally based on smaller weapons like the
Panzerfaust and
Panzerschreck, limited in the best case to ranges on the order of . X-7 was never fully developed before the war ended. In the immediate post-war era, the design was picked up by development teams in France and Australia. In France,
Nord Aviation's
Jean Bastien-Thiry developed an updated version of the X-7 using a
solid fuel rocket as the very small and highly portable
SS.10. Development started in 1948, with the first rounds fired in 1952. Evaluations by the
US Army in 1953 concluded it was not ready for operation, but that its progress should be tracked. The Army then instructed the
Redstone Arsenal to develop its own version of the basic concept, which emerged as the
SSM-A-23 Dart, a larger design with roughly twice the range of the SS.10. While the development of the Dart continued, Nord delivered a workable version of the SS.10, as well as the extended-range
SS.11. In the summer of 1958, the development of the Dart was canceled in favor of purchasing the two French designs. During the same period, the
British Army joined the Australian efforts to build a heavyweight long-range weapon, the
Malkara, with a range of about . The tracking system, similar to the SS.11, proved difficult to use and a new project started under the codename
Orange William to address this. This system used a computer to calculate the impact point, sending commands to the missile using an
infrared link. But the link was found not to work in smoke or dust, making it largely useless on the battlefield, and the project was abandoned.
New concept In January 1958, the Army's
Office of Ordnance Research and Development formed the Ad Hoc Working Group at the
Ballistic Research Laboratories (BRL) to define a future replacement for the SS.10 and 11. The team included members from
Picatinny Arsenal,
Frankford Arsenal,
Redstone Arsenal,
Watervliet Arsenal,
Detroit Arsenal and
Harry Diamond Laboratories. The group almost immediately decided not to attempt to define a weapon concept, and instead spend the next two years studying the problem while researching the possibility of using alternative guidance systems and continually watching foreign developments where the US was lagging. Meanwhile, aware of the British Army's dissatisfaction with the Malkara,
Vickers started a private design of a smaller weapon similar to SS.10 but with a greatly improved guidance system. The resulting
Vickers Vigilant was far easier to use in the field and required much less training. The Army, meanwhile, had come up with their own design that combined a system like the Vigilant with a much larger missile to produce
Swingfire. The goal was to allow the launcher to remain completely undercover while a gunner took a portable sight forward to aim at the targets from a concealed location. It was at some point during these early stages that the British became aware of the US developments. Having approved Swingfire to some degree based on the possibility of foreign sales, the emergence of a possible US competitor was a concern. Meetings between
Solly Zuckerman and
John H. Rubel led to the July 1961 Rubel-Zuckerman agreement, wherein the UK would continue development of the long-range Swingfire while the US concentrated on shorter-range missiles, up to , with new guidance systems. The US agreed to not introduce a system that competed directly with Swingfire or Vigilant without prior consultation but was free to develop new unguided "assault weapons" to replace the LAW. Both the US and
Canadian Army agreed to purchase Swingfire for the long-range role.
HAW Despite the efforts to reach an agreement over anti-tank missiles, in the early summer of 1961, the Chief of Ordnance asked BRL to deliver a formal definition for what was then known as the "Heavy Assault Weapon for the Long Range period", or HAW for short. They asked for a weapon to be delivered sometime between 1965 and 1970. BRL assigned the work to the Armored Systems Evaluation Branch of the Weapon Systems Laboratory. David Hardison, the Branch Chief, reconvened the Ad Hoc panel to review a long list of twenty-seven design proposals, all of which were found lacking. Hardison then began preparing a list of the ideal characteristics of a HAW weapon. Of primary importance was the adoption of some form of semi-automatic guidance, as the manual guidance systems (
MCLOS) of earlier weapons like SS.11 were found to be difficult to use as the relative movements of the launcher and target increased; MCLOS worked well for stationary launchers and slow-moving targets but had proven much more difficult to use from moving vehicles, and especially
helicopters. Experience with the
MGM-51 Shillelagh missile demonstrated that the simplest solution to successfully tracking the missile was to optically track a
flare attached to the missile using an
infrared seeker. This was essentially identical to a
heat seeking missile, but tracking its own missile rather than a separate target. Flares, however, were not ideal illumination sources, especially in the case where multiple rounds might be fired and the optical system might track the wrong one. In place of the flare, the panel selected an
infrared (IR) lamp whose output would be modulated with a shutter so each missile would have a unique signal. Using this style of guidance demanded that the missile be brought into the line-of-sight of the tracking system as soon as possible; in Shillelagh this was almost immediate because the missile was launched from a gun barrel directly into the view of the tracker. Earlier manual weapons like SS.10 and
ENTAC flew upwards after launch to clear the ground when being launched by infantry lying on the ground, and thus would not be immediately visible along the line-of-sight. To ensure the HAW could be tracked successfully, it would have to be launched from a tube, like Shillelagh, but one that was lightweight to ensure mobility. Finally, Shillelagh sent guidance commands to the missile using an infrared link, but as the British had discovered, this proved relatively unreliable in the field and was subject to countermeasures like random flashing IR lamps. For the shorter ranges envisioned for HAW, wire guidance was perfectly suitable and both much less expensive and largely immune to countermeasures.
TOW emerges of
Redstone Arsenal's proposed future HAW system (Heavy Antitank Weapon). The HAW ultimately resulted in the modern-day TOW. The resulting design was tube-launched, optically tracked, and wire-guided. BRL programmer Harry Reed immediately christened it "TOW", a name that the system carried into production. One problem that was noted early on was that the tube launch would make it difficult for the missile to be launched from a helicopter unless it was pointed relatively directly toward the target. Earlier systems were manually guided and did not need to be "gathered" quickly, so these were easier to launch at high crossing angles. Seeing this might be a major problem in the short term, TOW simply dropped the helicopter-launch requirement. When the BRL team returned the HAW/TOW study, the Pentagon gave them six months to come up with an actual requirement instead of a list of desirable features. Reed gathered submissions from the industry and quickly selected three contractors for further details,
Hughes Aircraft,
Martin Marietta, and
McDonnell Douglas. All three companies concluded the concept was able to be produced. On 12 January 1962, the BRL officially assigned the development of the TOW concept to the U.S. Army Missile Command (MICOM), who in turn formed the Antitank/Aircraft Weapons Commodity Office on 19 November 1962. In December 1962, Hughes was instructed to continue development while a development contract was being drawn up. Budget approval for development was granted in January 1963 as the XM65 TOW, and the final development contract, the first 100 percent cost-plus-incentive-fee, was signed on 3 May 1963. This led to the TOW Project Office opening on 1 October 1964. The British learned of the TOW program when it was sent to MICOM. In May, the US suggested they abandon Swingfire in favor of TOW, pointing out that the French were also introducing a long-range missile, and with three similar weapons in the marketplace, the British would find foreign sales difficult. However, the British Army was convinced that the launch vehicle would only survive if it was completely undercover, and TOW required the launcher to remain in sight of the target through the entire flight of the missile. They continued the development of Swingfire. In 1969, the House Authorization Subcommittee considered ending the TOW program in favor of the Shillelagh. A series of presentations by both missile teams followed, and ultimately the decision was made to continue both programs in September 1970.
Designs Three designs were returned for the initial selection, from Hughes, McDonnell, and Martin. Hughes' design used pop-out fins and a
gyroscope to allow it to automatically maintain an "up" direction. The wire spools were licensed from
Bofors and the rocket motor was made by Hercules. Guidance would be via flare tracking, using an internally-designed IR sensor based on their
AIM-4 Falcon efforts. McDonnell's entry did not attempt to control the spin of the missile, deliberately allowing it to spin during launch and flight like an artillery shell to improve accuracy. Like the Hughes entry, a gyroscope was used to define the up direction; in this case, this constantly changed relative to the missile body as it spun. The IR detector was placed at the end of a vertical V-shaped channel in the launcher. As gravity pulled the missile downward, it would begin to be blocked by the lower side of the V, causing the system to send commands to pull the missile upward. When it reached the top of the view at the end of the V, it stopped the up commands. The result was that the missile bounced up and down every of flight. Finally, Martin's missile used two side-mounted swept-back wings and a rocket that was split into two outlet tubes that were angled downward to give the missile natural lift during flight.
Hughes wins The initial production contract was awarded to Hughes on 28 June 1968, and the final contract on 29 November 1968. On 10 June 1969, Chrysler's Huntsville Division was awarded the second-source contract. Many problems emerged with the initial design, notably the early versions of the rocket motors which sometimes ejected burning bits of fuel, presenting a hazard to the gunners. MICOM suggested a new motor using "head end suspended double base" fuel from the
M72 LAW which solved this problem. The IR source had problems due to its use of a fine metal filament that ignited the
arc lamp which often broke during firing. Repeated tests and modifications solved this. The launch tube was designed to be sealed at both ends, with the rear seal being blown off by the rocket motor and the front by pressurized gas released by the guidance system's gyroscope. In practice, both proved unreliable, but remedial action solved the problems. Production began at USAF Plant #44 and the first production examples were delivered in August 1969. In September 1970 three training battalions had formed, and by 30 September 1970, the TOW had replaced the Army's existing heavy anti-tank weapon, the
M40 recoilless rifle. It increasingly replaced the French ENTAC missiles purchased earlier.
Helicopter launch In December 1963 the issue of helicopter launches was once again considered. The problem with the existing semi-automatic systems was that the missile had to be "gathered" by the optical tracker quickly for it to send commands to the missile. In contrast, earlier all-manual systems could be guided by the gunner at any time. With the TOW being launched from a tube, some other system would be needed to ensure it could be guided into the optics field of view after launch. This would be all the more difficult if the helicopter was not flying directly at the target, or was maneuvering. MICOM sent contracts to both Hughes and
Philco Ford, makers of the Shillelagh, to develop stabilized launch sights for their respective missile designs. They were in the form of a complete system combining the sighting system, launcher tube assembly, and all related equipment as the XM26 weapon system. Hughes won the contest in 1965 and was awarded a second development contract for XM26 in June 1966. XM26 was initially developed by a separate organization within BRL, the Aircraft Weapons Commodity Office. This was assigned to the TOW Project Office on 5 April 1970.
Replacement The U.S. Army is seeking a replacement for the TOW through the Close Combat Missile System-Heavy (CCMS-H) effort. Objectives are for a weapon with increased range out to or more, as well as greater speed, the ability to fire on the move, and lock on before and after launch capability while retaining similar launcher size and arming distance. The Army hopes to field the CCMS-H sometime between 2028 and 2032. ==Design==