HMS Illustrious will be in waters near Iran alongside the destroyer, Edinburgh, and a frigate, Westminster.
Earlier this year, 15 British service personnel were captured by Iranians as they searched a cargo boat in the Gulf.
The ships, accompanied by two minesweepers and three support vessels, will spend six months in the Gulf, the Indian Ocean and the Red Sea.
The MoD said the operation was about practising being a battle group.
Maritime security
A spokesman said: “The idea is to demonstrate our commitment to maritime security in a strategically very important part of the world.”
He added that the operation had been planned for a while.
For a month after the 15 servicemen and woman were seized in waters between Iran and Iraq in March, all boarding operations in the northern Gulf were suspended.
Two inquiries into the capture of those Royal Navy personnel by Iran identified “shortcomings” but said no one person was to blame.
