 Also under the command of the brigade were a number of US Army units, including 155 mm howitzers from the 90th Field Artillery Battalion, M4 Sherman tanks from 89th Tank Battalion and a company from the US 72nd Combat Engineer Battalion.By the time 3 RAR arrived in the theatre, the KPA had been broken and were in rapid retreat, with MacArthur's forces conducting a successful amphibious assault at Inchon and breakout from the Pusan Perimeter on the southern tip of the Korean peninsula.A steady advance began, driving the North Koreans northwards towards the 38th Parallel.