A British warship fired warning shots at a fast-approaching speedboat, possibly Iranian, in an unpublicized incident in April that adds to concerns about continuing tensions in the Persian Gulf, and the chance of an unintended outbreak of hostilities there.

The speedboat has not been identified, something the British defense ministry stressed when asked about the encounter. It could be an innocent misunderstanding or a Bahraini fishing boat, though a knowledgeable source who was shown the video says it has “all the appearances” of previous incidents carried out in the Gulf by Iranian speedboats. The confrontation is captured in a video obtained by The Daily Beast.

The video shows the speedboat powering parallel to the British warship HMS Iron Duke, which was patrolling off of Bahrain, and then turning directly towards it. Foghorns blaring, gunners on the Iron Duke then fired 100 yards to the side of the speedboat, causing its two crew members to duck and stop – they then wave at the British sailors as they speed away.

While talk in region remains focused on whether the United States or Israel will attack Iran, another large fear is the possibility of an unscripted, accidental war, spurred by a small clash that spins out of control. In January 7, 2008, five Iranian speedboats darted around three U.S. warships in the Straits of Hormuz in the Persian Gulf. No shots were fired. Then-President Bush said it was a provocative act. The Iranians said there was no confrontation. Conspiracy theorists muttered about a Gulf of Tonkin situation where a naval incident could be a pretext for wider hostilities.

U.S. commanders are specifically worried, however , about the lack of communication between the Western and Iranian navies, especially since Iran’s second navy, from the less traditional Revolutionary Guard, operates extensively in the Gulf. The United States had an agreement called “On the Prevention of Incidents On and Over the High Seas” with the Soviet Union during the Cold War to avoid the sort of muddled communications and missed signals that could lead to fighting. The U.S. Navy does not have that sort of agreement with Iran.

A U.S. official told me recently that accidental conflict is “always a concern, because we are only half the situation. We can control our half, our very professional officers out there. But you’ve got on their side people who are being rewarded for reckless behavior. An institution eventually gets the behavior it rewards. Iranian Republican guards have rewarded that kind of behavior for so long that they are going to get that kind of behavior.”

David Crist, a colonel who is an advisor to the Joint Chiefs of Staff, discussed at a conference in Washington in June how misunderstanding can occur. Stressing that his comments represented his own thoughts, rather than those of the U.S. military, Crist noted that Iran clearly feels U.S. ships are intruding on its waters in the Gulf.

“From the Iranians’ perspective, they have their own maritime boundaries, which the U.S. doesn’t accept,” Crist said. “The U.S. has occasionally and will intentionally violate that just to assert our right of passage. But from the Iranian perspective, they see that very much as a violation of their territorial waters. There are also a lot of other incidents that frankly we’re not quite sure what the rationale is. Recently, there have been two examples of an Iranian aircraft doing a Tom Cruise-esque fly-by of an American aircraft carrier and another one of one of our P3 navy aircraft. There’s a hot debate about what this means. Is this part of an Iranian plan to systematically harass U.S. naval forces or … is this just a hotshot pilot out doing what pilots sometimes do?”

The problem is that “the means to help de-conflict and de-escalate a crisis are simply not in place,” according to Crist. The United States does not have diplomatic relations with Iran and, said Crist, “the only communication with the Iranian Navy … is through demarches through the Swiss channel (Switzerland represents US interests in Iran) or through ship-to-ship bridge communications.”

A spokesman for the U.S. Fifth fleet told me from Bahrain that “in general our interactions with the Iranian navy are courteous and professional as befits any mariners operating on the open sea.” But besides these cases of camaraderie between sailors, a gap exists. Crist emphasized this again, when he said: “I think the U.S. doesn’t have a very good sense of what motivates Iranian security concerns.” This of course touches on big issues such as nuclear and missile tactics but “there’s also the degree of uncertainty about what individual Iranian commanders might do,” said Crist. The main cause of US concern, said Crist, “has been the Revolutionary Guards’ harassment of U.S. warships—a lot of this has been in the press over the years—which have created a lot of tension in some places and near exchange of gunfire.”

The video accompanying this article dramatically shows how this could happen. When I asked the British ministry of defence about this incident, the official answer was that “an unidentified small vessel made an unusually close approach at speed to HMS Iron Duke. In accordance with standard operating procedures, HMS Iron Duke took a series of escalatory preventative measures which resulted in warning shots being fired. The situation was resolved and both vessels went safely on their way.” Sources suggested that the boat could have been a piloted by Bahraini fishermen, who might have mistaken the lights and fog horns the British set off to warn the boat away as signs of greeting.

U.S. officials, though, are not so sure. They said that in any case the incident only highlights their worry that the Gulf is an aquatic tinderbox. And the Gulf is just one front with Iran while on others increasing Iranian aggressiveness worries U.S. military commanders. From caches of Iranian-made weapons found in Afghanistan to what sources say is funding of terrorist groups “doing malign activity” in Iraq and Afghanistan, Washington sees Iran as stepping up the pressure rather than dampening it down.

The Gulf, however, is the one place where Iranian and U.S., as well as other coalition forces, operate face-to-face with the Iranian military, rather than encountering each other through proxies. And so there is concern about conflicts flaring which no one wants.