But the mission failed. A watchman sounded the alarm and the ensuing gunfight forced the SEALs to retreat as US helicopter gunships circled overhead.

For SEAL Team 6, a special forces unit that entered the pantheon of US heroes with the killing of Osama Bin Laden in 2011, it was an unusual and embarrassing misstep showing that Somalia’s Al Shabaab militants are a stronger fighting force than some had assumed.