Board of Audit of Japan Warns Many MSDF P-1 Patrol Planes Inoperable; Parts Shortages, Device Defects Among Causes

The Yomiuri Shimbun

16:12 JST, June 28, 2025

Some Maritime Self-Defense Force P-1 patrol planes are not operational, according to a Board of Audit of Japan report released Friday.

P-1 patrol planes are for detecting submarines and surveilling suspicious ships in the seas around Japan.

The Board of Audit said that frequent engine trouble and shortages of parts for repairs are among the causes of the planes’ underutilization.

The report stated that “a limited number of planes are mission ready” and demanded the Defense Ministry improve the situation.

Thirty-five P-1 planes had been procured as of fiscal 2023 at a total cost of about ¥1.78 trillion. The government plans to procure another 26 units before fiscal 2054, when P-1 planes are set to cease operations.

In compiling the report, the Board of Audit checked the operational conditions of P-1 planes between fiscal 2019 and 2023 and concluded that they had been underutilized because of three factors: deterioration of engine performance; defects in electronic information-gathering devices; and a chronic shortage of replacement parts.

The report stated that, in many cases, the engine deterioration and electronic device defects were caused by material erosion due to long flights over the sea. There were many cases in which such planes became unusable.

Additionally, the low utilization rate was found to be caused by delays in procuring parts due to rapid changes in the global landscape and a worldwide semiconductor shortage.

As a result, some P-1 planes have had to undergo “cannibalistic maintenance” — in which parts of one P-1 plane are replaced with parts from others. Such units are utilized only in stopgap operations.

The Board of Audit did not disclose numerical data of the operations, names of defective devices and other details, as disclosing them could reveal the MSDF’s capability to deal with contingencies.

Speaking to reporters, a Defense Ministry official said, “We are taking the pointed-out facts seriously and will continue making efforts to maximize the operational levels [of P-1 patrol planes].”