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The US Army has canceled its planned upgrade of the Abrams tank, citing the tank's weight and vulnerability to enemy weapons, Defense News reported on Monday.

Stephen Bryen, a former Deputy Under Secretary of Defense and security strategy expert, confirmed that the Army believes the tank is no longer survivable on today's battlefield.

Heavy European tanks and armored vehicles have struggled in the mud and with fuel shortages in Ukraine. They have also been vulnerable to enemy fire. The Leopard tank, which was considered superior to the Abrams tank, has not performed well.

The Russians have destroyed around 15 Leopards using a variety of weapons, including artillery, helicopter-launched rockets, and drones.

The Leopard tank, which was billed as the next great thing to help Ukraine win the war, has proven to be a failure, according to Defense News.

Read more: Ukrainian soldiers complete M1 Abrams training in Germany: Politico

The failure of the Leopard tank in Ukraine raises concerns that the Abrams tank could also be vulnerable to Russian attacks, the report notes. 

Neither the Abrams tank nor the Leopard tank is equipped with active protection systems or reactive armor.

Russia able to destroy Leopard tanks easily

The Ukrainian army has hastily added reactive armor to some of the Leopard tanks that have been delivered to Ukraine, but this is a temporary measure and does not provide full protection against enemy fire.

The Leopard tank was designed with composite armor that was supposed to be able to deflect anti-tank weapons, including penetrating cannon rounds fired by enemy tanks or tandem warhead weapons.

However, the Russians have been able to destroy Leopard tanks fairly easily, even those that have been fitted with first-generation reactive armor.

The US is supplying depleted uranium (DU) shells to Ukraine for the soon-to-arrive Abrams tanks because DU shells are capable of penetrating any Russian tank.

Read more: US depleted uranium package to Ukraine to be announced soon: Reuters

US tanks lack active defenses

Russian tanks have so far been rarely exposed to enemy fire, as they have been using an active defense approach against the Ukrainian counter-offensive.

However, if Russia goes on the offensive, its tanks could be exposed to fire from Abrams tanks.

The effectiveness of the combination of depleted uranium (DU) shells and the Abrams tank is still unknown.

However, US tanks, like their Leopard counterpart, still lack active defenses.

The war in Ukraine has shown that the traditional concepts of tank warfare and tank survivability are no longer valid. 

Read more: US DoD to send $175 mil military aid package to Kiev