Banzai attacks was an extremely effective manoeuvre against most forces, however, eventually the charge became ineffective to the Chinese' superior melee training and the well-trained American forces armed with semi-automatic and automatic weapons. This tactic was first used against American forces during the Battle for Attu islands by Colonel Yasugo Yamazaki of the Japanese forces garrisoned there. Towards the end of the battle, he gathered all the remaining Japanese forces on the island and charged at the U.S. forces with a katana in hand. Although only 28 Japanese soldiers out of the 1,000 were taken prisoner (none of them were officers), the attack penetrated American defenses and shocked the rear-echlon units.
One of the largest Banzai attacks was made on Saipan on July 7, 1944 near the end of the battle. Approximately 4000 Japanese attacked two battalions of the 105th Infantry. The U.S. losses were 406 killed and over 500 wounded out of some 1100 involved. The Japanese lost upwards of 3000. However, most of the Japanese commanders chose not to use massive Banzai Charges during the war except as a final attack to avoid capture and dishonor. During the war, American soldiers usually made short work of Banzai Charges with automatic weapons and suppressing fire, although this was less successful during the night.