Ground Launched Small Diameter Bomb

The GBU-39 Small Diameter Bomb

Boeing, in partnership with Saab, developed an "inter-stage adapter" to connect the SDB to an M26 rocket.[12][13] Also providing expertise are two Norwegian companies, Nammo (booster rocket)[14] and Nordic Shelter (launchers).[15][10] The advantage of the M26 is that there is an abundant stockpile of these rockets.[16][17] Production of these rockets ceased in 2001, when 506,718 rockets had been produced.[18] As of 2004, 439,194 remained in total inventory. By 2007 the army was paying to destroy them.[19] The original ordnance carried by the M26 did not meet the terms of the Convention on Cluster Munitions (not signed by the United States).[14] Although the GLSDB can be launched from either MLRS or HIMARS, it also comes with its own launcher, which resembles a nondescript 20-foot (6.1 m) shipping container, making it easier to create decoys and more difficult for the enemy to locate and target.[20][21] After the rocket motor launches it to a high enough altitude and speed, the SDB separates from the rocket and the wings deploy, allowing the bomb to glide to its target.[12] The GLSDB carries a smaller warhead, with about one-third less explosives than is delivered with the existing GMLRS, depending on the type[17] (16 kg (35 lb)[22] vs 23 kg (51 lb)[23]). The company believed it could fill a gap for long-range precision fires while using its smaller warhead to save larger rocket munitions for strategic targets. While typical rockets from multiple launch rocket systems (MLRS) follow a ballistic trajectory, the rocket-launched SDB can be launched to altitude and glide on a selected trajectory.[24][12] Twelve M26 rockets at a time can be launched from MLRS, six at a time from HIMARS.[25]

Boeing and Saab Group conducted three successful GLSDB tests in February 2015. The system utilizes an existing weapon paired with a stockpiled rocket motor, while maintaining the loadout on a rocket artillery system. Unlike traditional artillery weapons, the GLSDB offers 360-degree coverage for high and low angles of attack, flying around terrain to hit targets on the back of mountains, or circling back around to a target behind the launch vehicle. The GLSDB has a range of 150 km (93 mi), or can hit targets 70 km (43 mi) behind the launch vehicle.[26][27][28] According to Saab, it is accurate to within one meter.[29] The weapon can be set to detonate above the ground or with a delay for deep penetration,[13] and is resilient to electronic warfare jamming,[13] which has been used extensively by Russia in eastern Ukraine since March 2014.[30]

In a 2017 demonstration, the GLSDB engaged a moving target at a distance of 100 km (62 mi). The SDB and rocket motor separated at altitude and the bomb used a semi-active laser (SAL) seeker to track and engage the target.[31] A 2019 test extended this range to 130 km (81 mi) against a target at sea.[11] The laser-guided SDB had previously been tested successfully using targets travelling at 50 miles per hour (80 km/h).[32]

The cost is undisclosed; however the SDB used in GLSDB has a cost to the U.S. military of about $40,000,[16][33] with the accompanying M26 rocket coming from obsolete inventory. The amount to be allocated to each GLSDB of the cost of the "inter-stage adapter", the cost to develop a launcher-container, and the other GLSDB development and production costs of Boeing and Saab is unknown.[34] For comparison purposes, the cost of a single M31 missile is estimated at $500,000,[17] though this may be the "export price", always higher than the amount charged to the U.S. army.[35] According to the U.S. army's budget, it will pay about $168,000 for each GMLRS in 2023.[36][37] The GLSDB is being offered to Ukraine as a long distance alternative to the 300 km (190 mi) ATACMS missiles,[38][39] which have a price per unit estimated to be well over $1 million.[40] The other long distance alternative is the 250 km (160 mi) Storm Shadow missiles,[41] each of which is estimated to cost around £2 million ($2.5 million,[42] fiscal year 2023). The U.K. has agreed to supply these to Ukraine.[43] The purpose in developing the weapons was to offer poorer countries the strike capacity of more expensive and advanced air forces. Jim Leary, director of global sales for Boeing, told reporters in 2019: “It really fits across a broader customer set because we’re taking an existing capability, maximizing it and creating an opportunity [for countries] that don’t have the ability to have a robust air force.”[44]

On 3 February 2023, the United States government announced an aid package for Ukraine as part of assistance during the 2022 Russian invasion of Ukraine that would include the GLSDB, which can be launched out of existing Ukraine-operated HIMARS or MLRS launchers (or out of its own launcher) to hit Russian targets that had been moved out of GMLRS range. The GLSDB almost doubles the range that Ukraine could previously target with these launchers (150 km (93 mi) vs 85 km (53 mi) with GMLRS).[45][18] This "will put all of Russia's supply lines in the east of [Ukraine] within reach, as well as part of Russian-occupied Crimea", according to Reuters.[46]

According to a retired colonel of the Luhansk People's Republic (a region of Ukraine illegally annexed by Russia),[47] the GLSDB will be much slower and easier to target than the existing GMLRS since it is a glider whereas the GMLRS arrives by rocket power.[48][49] However, according to Saab the glider will be more difficult to intercept since it can be programmed to approach a target from any direction, and from a variety of angles.[17] Unlike conventional artillery that follows a predictable path from launch to destination, the wings and navigation ability of the GLSDB allow it to evade obstacles and anti-air defenses by steering around them, even approaching from the target’s rear.[50][12] Also, because the GLSDB is a glider it has little IR signature, making it a poor target for IR homing missiles such as MANPADS.[51] This will mark the weapon's first export and use in combat. When originally announced it was estimated that it might take up to nine months to develop a ground-launched version but Boeing announced that it could possibly be delivered as early as spring of 2023.[52][53][54][55]

On 28 March, Russia state media claimed that a GLSDB had been shot down by air defences, without saying where, only that it happened in the last 24 hours.[56]

On 30 March, Taiwanese media reported that Taiwan has deferred purchasing GLSDB so that it could be sent to Ukraine. This was done at the request of the United States. The weapon has only entered "initial mass production stage" in 2023.[57] The narrowest part of the Taiwan Strait is 130 km (81 mi; 70 nmi) wide,[58] within the range of the GLSDB and making it more difficult for the PLA to assemble an amphibious force to invade Taiwan.[59]

On 22 June, Laura Cooper told Congress that because of delays caused by development and production issues, Ukraine would receive GLSDB missiles "no earlier than autumn".[38]

On 14 October 2023, Boeing said that the GLSDB will be delivered to Ukraine by winter.[60]