Well it seems our first impression was the truth. There was a terrorist attack on a Japanese ship in the Persian Gulf last month. At the time Iran suggested that the ship was hit by a tidal wave or some other nonsense, despite the gaping hole from the explosion...
I suspect Iran was involved..
http://www.usatoday.com/news/world/2010-08-06-oil-tanker-attacked_N.htmUAE: Japanese oil tanker was attackedDUBAI, United Arab Emirates (AP) — An explosive-laden dinghy had struck a Japanese oil tanker in the Persian Gulf last month, the Emirati state news agency said Friday, in the first official confirmation that the incident was an attack.
The report came after an obscure al-Qaeda-linked group said Wednesday one of its suicide bombers had hit the tanker to avenge the plunder of Muslim wealth. If true, the claim by the little-known Brigades of Abdullah Azzam would mark the first time the terror network has attacked the Japanese.
Emirates' WAM news agency on Friday quoted an unnamed government official as saying the investigation revealed traces of homemade explosives on the hull of the tanker.
WAM said investigators believe a small boat with explosives had approached the tanker. It said the explosives find "indicates the tanker was subjected to a terror attack."
There have been conflicting reports about what happened to the M. Star supertanker, which was damaged July 28 in the Strait of Hormuz— a transit point for about 40% of tanker-shipped oil worldwide.
A crewmember was injured and the vessel sustained a square-shaped dent on the rear side of the hull during the incident. The Marshall Islands-flagged ship, loaded with 270,000 tons of oil, was heading from the petroleum port of Das Island in the United Arab Emirates to the Japanese port of Chiba outside Tokyo.
In its claim posted on militant websites, the al-Qaeda-linked group carried a photo of the purported bomber pointing to a photograph of a tanker on a laptop. It said the bomber was a "martyr" — meaning he had died in the attack. It also said it had delayed the announcement until several group members who were involved in the operation "returned safely to base."
The WAM report said the vessel left the Emirati port of Fujairah on Friday after damages to the hull were fixed.
The Brigades have in the past claimed responsibility for the August 2005 firing of Katyusha rockets that narrowly missed a U.S. amphibious assault ship docked at Jordan's Aqaba Red Sea resort but killed a Jordanian soldier. It had also claimed the July and October 2004 bombings at Egypt's Red Sea resort of Sharm el-Sheik and two other resorts that killed a total of 98 people.
al-Qaeda has carried out attacks on oil infrastructure on land in nearby Saudi Arabia, as well as a 2002 suicide bombing against a French oil tanker off the coast of Yemen and the 2000 bombing of the USS Cole in the Yemeni port of Aden.