The GBU-39 Small Diameter Bomb air-to-ground munition is a light gliding and guided bomb, intended to destroy various objectives, ranging from reinforced positions to armored vehicles, while limiting damage and collateral losses. With a mass of 129 kg, it has a system of fins which deploy after release allowing it to reach targets up to 110 km away, or 75 km for mobile targets. Derived in several variants, it carries different military loads of different nature and power depending on the mission and the target, as well as guidance which can be inertial coupled to the GPS, laser or radar signal.
One of the advantages of the GBU-39, and its gliding trajectory, is to be able to maneuver close to the objective to, for example, attack the target from an appropriate angle of attack. This is precisely why Boeing, which joined forces with the Swedish Saab for the occasion, developed a ground-to-ground version of this ammunition, combining a rocket booster with the GBU-39 to provide the altitude and muzzle velocity allowing it to reach targets up to 130 km away. The assembly is embarked in an autonomous launch container, or in an M26 launch tube fitted to the M270 or HIMARS.
Tests of the Ground Launched Small Diameter Bomb, or GLSDB, which began in 2015, showed promising capabilities in terms of range and precision, as well as flexibility of use. Indeed, the GLSDB can easily be carried and decommissioned from a vehicle or a ship, offering increased firepower at a relatively low cost in terms of performance. In fact, it could, in a relatively short time, fill certain deficiencies that American artillery faces today, pending the entry into service of the new indirect fire systems, one of the major programs currently underway. the US Army.
The fact remains that, if GLSDBs have an interesting range and precision, they also have, like all gliding munitions, a notable weakness, their low speed. Indeed, a hovering gravitational bomb moves between 250 and 300 knots, making it vulnerable to close defense systems, such as the Russian Pantsir or Tor M2. To counter this vulnerability, air attacks use several GBU-39s simultaneously, significantly reducing the probability that a CIWS can eliminate them all, and therefore prevent the destruction of the target it was intended to protect. It will probably be necessary to consider a similar procedure for GLSDBs, as soon as the adversary uses close protection systems. In addition, the procedures for identifying and designating targets must be adapted to land or naval use, very different from those carried out from an aircraft.
However, with the GLSDB, the US Army could have an interesting and inexpensive interim solution to quickly increase its firepower in the depth of the adversary's device. Its ability to be implemented from autonomous launch containers also makes it possible to disperse these vectors, and therefore reduce their vulnerability. Above all, this would allow American forces to have the benefits of close air support, without having to have this air support, for whatever reason.
However, we will have to wait for a possible order for the system by the US Army, which, as we know, is currently facing numerous modernization programs, each more expensive than the other, and yet all equally essential. Despite its indisputable qualities, it is therefore not certain that the American Army will acquire the weapon system from Boeing and Saab.
