Some did not have formal education, and others were fluent only in their own languages and dialects.
The pioneer batch of national service (NS) trainees - who were enlisted on Aug 17, 1967 - were not an easy bunch to train, recounted one of the instructors, retired senior warrant officer Ong Hui Pheng, 79.
"We went to the extent of forming a 'Hokkien platoon'," he added.
But they bonded as they worked towards the common purpose of defending Singapore: the start of an NS institution that has lasted 50 years.
Mr Ong, then a regimental sergeant major with the 3rd Singapore Infantry Regiment, said it was not easy to get the trainees to accept the concept of NS. Laws passed in March 1967 to make NS compulsory were initially met with resistance.
"Not every citizen accepted that (NS) concept... to serve for two years with an allowance of $60 every month," Mr Ong said yesterday.
Mr Ong was one of the 98 NS pioneers and their trainers invited yesterday to the Basic Military Training Centre on Pulau Tekong to witness the launch of NS50, a year- long celebration to commemorate 50 years of NS.
Despite the initial resistance, Mr Ong found a way to motivate his recruits. "If I tell them to run, I will run first. If I tell them to eat, I will eat last. That was leadership by example," he said.
Retired lieutenant-colonel Albel Singh, 68, one of Mr Ong's trainees, said the enlistees built up a camaraderie because they were thrown in at the deep end.
Mr Singh, who later signed on, remembers being deployed as an officer cadet to conduct vehicle patrols in Tai Seng, in the Paya Lebar area, during the May 1969 racial riots.
Mr Singh, who was first in line to register for NS on March 28, 1967, said: "Foreign influences can affect the stability of the country and at any time cause problems."