context: Seabees deployed to Vietnam twice in the 1950s. First in June 1954 as elements of Operation Passage to Freedom and then two years later to map and survey the nations roads. Seabee teams 501 and 502 arrived on 25 Jan 1963 and are regarded as the first Seabees of the Vietnam conflict. They were sent to Dam Pau and Tri Ton to build camps for the Special Forces. In June 1965, Construction Mechanic 3rd Class Marvin Glenn Shields was a member of Seabee Technical Assistance Team 1104, that took part in the Battle of Dong Xoai. He was posthumously awarded the Medal of Honor for his actions there and is the only Seabee ever to be awarded the Medal of Honor. Those Seabee "Civic Action Teams" continued throughout the Vietnam War and often were fending off enemy forces alongside their Marine and Army counterparts. Teams typically built schools, clinics or drilled wells. In 1964 ACB 1 was the first CB in the theatre. Beginning in 1965 Naval Construction Regiments (NCRs) deployed throughout Vietnam. The Seabees supported the Marines by building a staggering number of aircraft-support facilities, roads, and bridges. Seabees also worked with and taught construction skills to the Vietnamese people. In 1968 the Marine Corps requested that the Navy make a name change to the CBs. The Marines were using "MCB" for Marine Corps Base and the Navy was using "MCB" for Mobile Construction Battalions. The Navy then added "Naval" to MCB creating the NMCBs that now exist. In May 1968 two reserve battalions were activated (RNMCBs 12 and 22) which brought the total number of battalions rotating to Vietnam to 21 (not including ACBs 1 and 2 or the two Construction Battalion Maintenance Units (CBMUs) that were there too). During 1969 the total number of Seabees that had deployed topped out at 29,000 and then their draw-down began. The last battalion withdrew the end of 1971 which left 3 Seabee teams. They were out by at the end of 1972.
question: How many battalions were rotating to Vietnam in April 1968, not including ACBs 1 and 2 or the two Construction Battalion Maintenance Units??
answer: 19