He served as a midshipman on the cruiser Iwate, which made a long-distance navigational training voyage to Hong Kong, Singapore, Australia, New Zealand and the South Seas Mandate in 1915.

In the 1930s, Iwabuchi served as chief gunnery officer on a number of vessels, including the cruisers Ōi in 1930, Abukuma in 1931, and Chōkai in 1932, and the battleship Hiei in 1933.

This would normally have been a dead-end position to his career; however, the increasingly desperate war situation provided Iwabuchi with a final opportunity.

Yamashita wanted to consolidate his forces, and to avoid being trapped in urban warfare in downtown Manila with close to a million civilians.

Together with the under-equipped and ill-disciplined 15,000 marines and 4,000 Imperial Japanese Army stragglers under his command, he found several good defensive positions in the historic Intramuros area of the old city of Manila, including the massive walls of colonial Fort Santiago.

After many days of building-to-building combat, more than 16,000 Japanese defenders were killed, and by 26 February Iwabuchi committed suicide at his command post, using a pistol pointed to his mouth,[1][better source needed] although his body was never positively identified.