The surviving "Ferdinands" fought various rear-guard actions in 1943 until they were recalled to be modified and overhauled, partially based on battle experience gained in the Battle of Kursk. Returned to the Nibelungenwerke factory in Austria, on 2 January 1944, upgrades commenced on 48 of the 50 surviving vehicles. The most visible exterior upgrades were 1) the addition of a ball-mounted MG 34 in the hull front, 2) a new commander's cupola (modified from the standard StuG III cupola) for improved vision, 3) re-designed armored engine grates (for better bullet and shrapnel protection) and 4) the application of "Zimmerit" anti-magnetic mine paste.