Overview

• Kawasaki told the Defense Ministry that some diesel engines for JMSDF submarines manufactured through 2021 likely involved improper fuel‑efficiency test data, and an external investigation is underway.
• The suspected practice involved rewriting measured values from post‑assembly trial runs to meet specifications requested by the Defense Ministry, according to reporting based on sources.
• Irregularities are feared to date back about two decades and could touch many in‑service Taigei‑ and Soryu‑class boats, with all submarine engines in the 25‑strong fleet supplied by Kawasaki.
• The company says it sees no current impact on submarine operation or safety and has pledged to publish results promptly and reinforce prevention measures once the probe concludes.
• The submarine findings emerged as Kawasaki was investigating ship‑engine data falsification disclosed in August 2024, and they follow separate scandals over fabricated subcontracting and illicit funds tied to submarine repairs; the defense minister called the situation very regrettable.