At 18:00 on 16 March (25 days after the landings), the 5th Marine Division still faced Kuribayashi's stronghold in a gorge 640 m (700 yd) long at the northwestern end of the island. On 21 March, the Marines destroyed the command post in the gorge with four tons of explosives and on 24 March, Marines sealed the remaining caves at the northern tip of the island.
However, on the night of 25 March, a 300-man Japanese force launched a final counterattack in the vicinity of Airfield No. 2. Army pilots, Seabees and Marines of the 5th Pioneer Battalion and 28th Marines fought the Japanese force for up to 90 minutes but suffered heavy casualties (53 killed, 120 wounded). Two Marines from the 36th Depot Company, an all-African-American unit, received the Bronze Star. 1st Lieutenant Harry Martin of the 5th Pioneer Battalion was the last Marine to be awarded the Medal of Honor during the battle.
Although still a matter of speculation because of conflicting accounts from surviving Japanese veterans, it has been said that Kuribayashi led this final assault, which unlike the loud banzai charge of previous battles, was characterised as a silent attack. If ever proven true, Kuribayashi would have been the highest ranking Japanese officer to have personally led an attack during World War II.
Additionally, this would also be Kuribayashi's final act, a departure from the normal practice of the commanding Japanese officers committing seppuku behind the lines while the rest perished in the banzai charge, as happened during the battles of Saipan and Okinawa.
The island was officially declared secure at 09:00 on 26 March.