The 133rd CB and the 4th Marine Pioneer Battalion were the primary units of the "Assault" shore parties for the 23rd and 25th Regimental Combat Teams (RCT) on the 4th Marine Division's yellow and blue beaches. The 4th Marine Division's single Pioneer Battalion was assigned to the 25th RCT. USMC tactical operations required another Pioneer battalion for the 23rd RCT's Assault. The 121st CB had been tasked as such at Roi-Namur, Siapan, and Tinian so giving that task to the 133rd was simply standard 4th Marine Division operations. Tasking Seabees for USMC shore party at Iwo was a fortuitous decision for the Corps. The CBs brought organic elements the Marines did not have, specifically, bulldozers with winches and D8s 132–148 Hp compared to the Marine Corp's TD 18s 72–80 Hp. Afterwards, the after action reports recommended all USMC bulldozers be equipped with winches as they had none. The history is, that "on the beach at Iwo, bulldozers proved to be worth their weights in Gold" and the CBs had the biggest and the best the Navy could provide. The entire 1st Battalion 24th Marines (1/24) replacement draft that was attached to the 133rd.