bore sight alignment device. Stowage of 155mm rounds increased from 28 to 36 rounds; .50cal ammunition remained at 500 rounds. During M109A2 production, a slightly simplified version was also produced for export. This had minor internal changes and deleted the hull flotation feature. These were designated M109A1B. M109A3 and M109A3B M109A1s and M109A1Bs rebuilt to M109A2 standard respectively. Some A3s feature three contact arm assemblies, while all A2s have five. M109A4 M109A2s and M109A3s improved with Nuclear, Biological, and Chemical / Reliability, Availability, and Maintainability (NBC/RAM) improvements, including air purifiers, heaters, and Mission Oriented Protective Posture (MOPP) (protective) gear. The traversing mechanism's clutch was hydraulic, as compared to the electric mechanism on previous M109s, and featured a manual override. The M109A4 gained a second hydraulic filter, and also included an improvement to the engine starting equipment which greatly improved the ability to start in an emergency. Ammunition stowage remained the same as in previous models. M109A5 Replaces the 155 mm M185 Cannon in an M178 Mount with a 39-caliber 155 mm M284 Cannon in an M182 Mount, giving the A5 a maximum range of 22,000 meters with unassisted projectiles and 30,000 meters with Rocket Assisted Projectile (RAP) rounds. The vehicle can carry 36 complete rounds of ammunition and has a 440 hp engine instead of the standard 405 hp engine. M109A5+ Various manufacturers have upgraded the fire control and other components of the M109A5. BAE Systems in York PA recently delivered 12 M109A5+ vehicles to Chile and 40 M109A5+ vehicles for Brazil. M109A6 "Paladin" The Paladin model has improvements in the areas of survivability, RAM, and armament. This includes increased armor, a redesigned internal arrangement for safer ammunition and equipment storage, engine and suspension upgrades, and improvement of the M284 Cannon and M182A1 Mount. The greatest difference is the integration of an inertial navigation system, sensors detecting the weapons' lay, automation, and an encrypted digital communication system, which utilizes computer controlled frequency-hopping to avoid enemy electronic warfare and allow the howitzer to send grid location and altitude to the battery Fire Direction Center (FDC). The battery FDCs coordinates fires through a battalion or higher FDC. This allows the Paladin to halt from the move and fire within 30 seconds, with an accuracy equivalent to the previous models when properly emplaced, laid, and safed—a process that previously required several minutes under the best of circumstances. Tactically, this improves the system's survivability