The U.S. Army accepted their first M109 in 1963. The M109 sported the short barrel (23 Caliber) 155mm M126 gun. Since 1963 the M109 has gone through a series of changes and upgrades. Most notable is the change to the longer barreled (39 Caliber) M185 gun on the M109A1 and the removal of the external floatation kit and addition of the external ammunition storage box on the M109A2.
The Israelis received their first 60 M109s in 1967. After years of boycotts, refusals, and subterfuge, the United States agreed to openly sell Israel much needed modern armored fighting vehicles. The only changes the IDF did to the original M109s were to add some hull mounted crew rails on the side and the conversion of some muzzle brakes to the Soltam version (probably for testing purposes).