Constable is one of the junior ranks in the Toronto Police Force and in Flashpoint. Excluding Gregory Parker, Roland Cray and Troy, all other SRU members were Constables. Only at the end was Ed Lane promoted to the rank of Sergeant).
In Flashpoint, despite all the SRU members being Constable, each of them have different skill sets and seniority. For example, Ed Lane and later Donna Sabine were Team Leaders, but they still held the rank of Constable. Jules Callaghan was a profiler, deputy negotiator and sniper. Mike "Spike" Scarlatti was an explosives and electronics expert. Sam Braddock was primarily a sniper along with Ed, although Ed was senior to him in terms of leadership and only at the end was Sam promoted to Team Leader. Wordy had no specific role but was often partnered with Ed. Lou had no specific responsibilities similarly Raf.
All SRU Despatchers such as Kira Marlowe and Winnie Camden were also ranked as Constable.
In reality, the Toronto police force has different tiers/levels of Constable, although that is not stated in Flashpoint [1].