Al-Shabaab raid at Manda Airfield in Kenya caught US military unprepared, AFRICOM commander Stephen Townsend has said.
Three Americans died during the January 5th attack, which left the US military badly exposed in her determination to help allies.
The six-hour fight with the militants left six aircraft meant for sophisticated surveillance dismembered, even as Al-Shabaab claimed responsibility.
The armed militants disconnected power within the vicinity of Manda Airfield and Camp Simba before raiding the base, residents said, according to AFRICOM.
While appearing before Senate Armed Forces Committee, Gen Townsend admitted laxity on the elite forces, adding that "we are digging to find why that is the case".
He said: “We were not as prepared there at Manda Bay as we needed to be. Al-Shabaab managed to penetrate on to that airfield."
Besides the three casualties, two servicemen were badly wounded and were subsequently airlifted to Djibouti for advanced treatment, Military Times reported.
Manda Airfield attack was the first successful raid by the militants in an American base within Africa.
Last year, there was an attempted raid at Ballidogle army base in Somalia but it was expeditiously repulsed.
Eleven militants were killed, authorities said.
Although the US maintained that only three people died; a serviceman and two contractors, Al-Shabaab has disputed the figures.