The most effective variant of the Zero was the Model 52. It had shortened wings to increase speed and the folding wing mechanism was eliminated. Fuel tanks received carbon dioxide fire extinguishers and one 13.2 mm Type 3 machine gun was added in each wing. The 7.7 mm gun on the left side of the cowl was deleted and four racks for rockets or small bombs were installed. Armored glass was installed and a thick plate of armor was installed behind the seat. The wing skin thickness was increased and due to the weight gain, this variant was used mainly for intercepting B-29s.