As production continued, the Typhoon's role changed from a low-level interceptor fighter to a fighter bomber. Racks capable of carrying bombs were fitted to the wings from October 1942 and were first used operationally by 181 Squadron. By mid-1943, all Typhoons off the production line were capable of carrying bombs. Bigger, solid rubber, grooved "anti-shimmy" tail wheel tyres were introduced in March 1943 on all Typhoons from the 1,001st production aircraft, "EK238". The new tyres helped to make heavier, bomb-laden Typhoons more manageable during ground manoeuvres. With the introduction of the bomb racks, small extensions were added to the cannon shell case ejector slots. These allowed the casings to drop clear of bombs or drop tanks suspended from the wing racks. Because of the vulnerability of the Typhoon's liquid-cooled engine cooling system to ground fire, some of armour was added, lining the sides and bottom of the cockpit and engine compartments, as well as the radiator bath.