My ex-colleague was a NS Guard Specialist (He share with me more then 10 years ago & if I remember clearly, he was a NSF platoon sergeant with the rank of 2SG) & he went to Recruitment centre to sign up for Commando. After he clear his interview & medical checkup, he needs to clear his selection test (Related to Infantry such as river crossing & etc). After passing selection & signing of contract, he will needs to go for courses like CSLC, BAC & 1 relevant vocational course. He start his commando career as a detachment commander with the rank of 2SG & he do not needs to go for platoon sergeant course again.