An added strain to United States-Japan relations at the wrong moment has been created by what is being called here "the case of the hit-and-run submarine." Foreign Minister Masayoshi Ito, meeting April 11 with US Ambassador Mike Mansfield, asked Washington to investigate thoroughly an accident in which a small Japanese freighter sank after colliding with the US nuclear-powered ballistic missile submarine George Washington in the East China Sea April 9.
The 2,350-ton Nissho Maru, its hull opened by the submarine's conning tower, went down within minutes, with 13 of its 15 crewmen escaping. The sub suffered only minor damage.
But the incident has quickly brewed up into a political storm for several reasons:
* It took the United States more than a day to notify Japanese authorities of the collision.
* The freighter's crew have claimed neither the submarine nor a US military aircraft circling overhead made any rescue attempt.
* Questions have been raised about why the submarine was so close to Japanese territory and whether it was carrying any missiles. (It has a capability to carry 16 Polaris missiles each armed with three warheads.)
Two Japanese destroyers picked up the survivors after 18 hours adrift.
The crewmen said that shortly after they boarded life, rafts, a black submarine surfaced near them, but then disappeared. A propeller-driven plane with US insignia circled overhead but apparently failed to see them.
An official American statement to Japan, expressing regret for the incident and promising a full investigation, said the George Washington surfaced immediately after the collision to offer assistance, but saw nothing because of rain and fog. Unaware the ship had sunk, the US did not tell Japan of the collision until the crewmen were rescued.
Japan's concern was intensified by the fact that the collision occurred less than 20 miles outside its 12-mile territorial waters.
The US has refused so far to explain what the submarine was doing in the area. There is speculation that it was part of a joint military exercise with Japan.
Government officials have expressed doubt the George Washington was carrying any Polaris missiles at the time.
But fears of what would have happened to Japan if the submarine's reactor or missiles had been damaged are a major element in the criticism being heaped on the United States.
The collision could not have come at a worse time -- less than a month before Prime Minister Zenko Suzuki visits Washington.
A key issue will be American desires for Japan to play a larger military role. Mr. Suzuki is not against the idea, but feels he has to move in step with conservative public opinion at home demanding more welfare, not defense, spending. Opposition parties continue to attack any government move suggesting a stronger US-Japan military cooperation.
The nuclear issue is particularly sensitive. The government often is asked to check allegations that the US is storing nuclear weapons at its Japanese bases in direct contravention of this co untry's nonnuclear principles.