XM291

{{Infobox weapon

| name = XM291

| image =

| caption = CATTB with the 140 mm XM291

| origin = United States

| type = Tank gun

| is_artillery = Yes

| caliber = 140 mm / 120 mm

}}

The XM291 Advanced Tank Cannon (ATAC) is an American experimental 120 or 140 mm smoothbore tank cannon. It started development in 1991 as a way to substantially increase the performance of tank cannons against the perceived threat of future Soviet main battle tanks. It can be used in two configurations, one in 140 mm and one in 120 mm electrothermal-chemical technology (ETC).{{Cite book |last=Defense |first=United States Congress Senate Committee on Appropriations Subcommittee on |url=https://books.google.com/books?id=vRREAQAAMAAJ&dq=XM291+Advanced+Tank+Cannon&pg=PA154 |title=Department of Defense Appropriations for Fiscal Year 1994: Hearings Before a Subcommittee of the Committee on Appropriations, United States Senate, One Hundred Third Congress, First Session |date=1993 |publisher=U.S. Government Printing Office |isbn=978-0-16-043658-1 |pages=154–155 |language=en}} The XM291 was the first cannon to incorporate a system that counteracted the vibrations in the barrel caused by the tank moving over terrain, using the dynamically tuned shroud (DTS).{{Cite book |last1=Littlefield |first1=Andrew G. |url=https://www.angelfire.com/ny5/littla/Papers/Littlefield_ASC2002_CA03.pdf |title=GUN BARREL VIBRATION ABSORBERS FOR MEDIUM AND LARGE CALIBER SYSTEMS |last2=Kathe |first2=Eric L.|url-status=live |archive-url=https://web.archive.org/web/20190810060727/http://www.angelfire.com/ny5/littla/Papers/Littlefield_ASC2002_CA03.pdf |archive-date=2019-08-10 }}

While it was originally developed for the Block III tank, development of the Block III was halted while the XM291 saw continuous development and was used on other testbeds such as the CATTB and the M1 Thumper.{{Cite book |last1=Zaloga |first1=Steven |title=M1 Abrams Main Battle Tank 1982–92 |last2=Sarson |first2=Peter |date=28 January 1993 |isbn=1855322838 |pages=14|publisher=Bloomsbury USA }}