conscription not enforced
The Puerto Rican armed forces are incorporated into the armed forces of the USA. This is because of the special status Puerto Rico has within the USA, for, according to the 1952 Constitution, Puerto Rico is a "free state associated with the USA". Puerto Ricans are granted US citizenship, although they are not allowed to take part in US elections (they may take part the elections for the Governor of Puerto Rico).  
Puerto Ricans are subject to the US legislation on military service, which means registration for the US armed forces is compulsory for all young men. 
In the past, when conscription in the US armed forces was enforced, many Puerto Ricans did not register, but very few were sent to prison for refusal.
Owing to the general poverty in Puerto Rico an army career is an appealing career option for many young men. About 3,000 mainly poor Puerto Ricans join the US armed forces annually.
During the Vietnam war, 54 per cent of the US figthing troops were said to consist of Puerto Ricans. 
For details on the US legislation on conscription and conscientious objection, see the respective country report on the USA.
 Lindsay-Poland, John, and Matt Meyer 1994. Gegen den Status Quo in Lateinamerika, in: Kriegsdienstverweigerung in Lateinamerika, KDV im Krieg, Connection e.V., Offenbach.  UNHCR Centre for Documentation and Research, 12 January 1993. [3 ] Prasad, D., T. Smythe 1968. Conscription: a world survey, compulsory military service and resistance to it. War Resisters' International, London.