The flaw in the Chinese plan was a lack of accurate intelligence about the UN forces. Even though the US X Corps was stretched thin over northeast Korea, the slow Marine advance allowed the bulk of the US 1st Marine Division, including the 5th Marine Regiment (United States), 7th Marine Regiment (United States) and 11th Marine Regiment (United States), to be concentrated at Yudami-ni. Furthermore, the strategically important Hagaru-ri, where a Douglas C-47 Skytrain-capable airfield was under construction and a supply dump, was not a priority for the Chinese despite being lightly defended by the 1st Marine Regiment (United States) and 7th Marines. Only Task Force Faith (RCT-31), an understrength and hastily formed regimental combat team of the US 7th Infantry Division, was thinly spread along the eastern bank of the reservoir. Those units would later take the brunt of the Chinese assaults. As for the UN forces, the 1st Marine Division had an effective strength of 25,473 men at the start of the battle, and it was further reinforced by the British 41 Commando and the equivalent of two regiments from the 3rd and 7th Army Infantry Divisions. The UN forces had a combined strength of about 30,000 men during the course of the battle. The UN forces at Chosin were also supported by one of the greatest concentrations of air power during the Korean War, since the 1st Marine Air Wing stationed at Yonpo Airfield and five aircraft carriers from the US Navys Task Force 77 (U.S. Navy) were able to launch 230 sorties daily to provide close air support during the battle, while the US Air Force Far East Combat Cargo Command in Japan reached the capacity of airdropping 250 tons of supplies per day to resupply the trapped UN forces.
Question: How many Marine Regiments did the US 1st Marine Division comprise of?
Answer: 3