On November 17, a British F-35B Lightening II fighter jet from the Royal Navy flagship aircraft carrier, HMS Queen Elizabeth, crashed into the Mediterranean Sea.

The UK’s Ministry of Defense said that the fighter jet pilot ejected during a routine operation. The incident occurred at approximately 10 am UK time in international waters. No other vessels or aircraft were involved.

“The pilot has been safely returned to the ship and an investigation has begun, so it would be inappropriate to comment further at this time,” the ministry’s Press Office said on Twitter.

The F-35B short-take-off, vertical-landing fight jet was one of 24 so far delivered to the UK. Each of the American-made stealthy jets costed the UK around £100 million.

The incident took place as HMS Queen Elizabeth was its way back from its maiden operational deployment, which was in the Far East. The flagship was carrying eight British F-35B fighter jets, along with ten American F-35s.

The UK military has pledged to purchase as many as 138 F-35 fighter jets. Only 48 are currently on demand. The incident may effect these plans, which are already expected to face cuts.

The design and performance of the F-35 have been facing much criticism. In March, a F-35B of the US Marine Corps was significantly damaged when a round fired from its underbelly 25 mm gun pod exploded shortly after leaving the muzzle of the cannon mounted within.