The UK is to send a second warship to the Gulf amid escalating tensions with Iran.
HMS Duncan, a Type 45 destroyer, will join HMS Montrose which is due to go in for "pre-planned maintenance" while continuing its deployment.
The move is understood to have been long-planned but was brought forward by a number of days.
Earlier this week, the Ministry of Defence said Type 23 frigate HMS Montrose saw off three Iranian boats which tried to stop a British tanker in the Strait of Hormuz.
Iran denied the incident happened.
A Government spokesperson said: "As part of our long-standing presence in the Gulf, HMS Duncan is deploying to the region to ensure we maintain a continuous maritime security presence while HMS Montrose comes off task for pre-planned maintenance and crew change over.
"This will ensure that the UK alongside international partners can continue to support freedom of navigation for vessels transiting through this vital shipping lane."
The US, who earlier this year deployed a carrier strike group and extra personnel to the region, has called for an international military coalition to help protect the Gulf's waters.
The Government stressed HMS Duncan's deployment is not in response to a request from the US or as part of a coalition force.
A Downing Street spokeswoman said they are "concerned" about threats Iran are making "to disrupt shipping in the area".
"We have been urging them to de-escalate the situation in the region," the spokesperson told a Westminster briefing.
Along with Montrose, the Navy has four mine countermeasures vessels and the Royal Fleet Auxiliary Cardigan Bay logistics ship in the region.
Iran has warned Britain is playing "a dangerous game" as the country demands the immediate release of an oil tanker which was seized by Royal Marines off the coast of Gibraltar.
The territory's chief minister said the vessel contained 2.1 million barrels of light crude oil.
The Iranian supertanker was seized last week as it was believed to be delivering oil to Syria, in breach of EU sanctions.
Iran again denied this was the case.
US relations with Iran have also worsened since President Donald Trump pulled the US out of a nuclear deal with Iran and reinstalled sanctions.