Old Sweat is correct about the bastardization of the corporals and captains being a pay issue.
Most of you weren't even born, but we had a series of fairly sharp recessions in the 1950s that played havoc with the nation's finances. One or two people here will recall 'Dief the Chief's (Prime Minister John Diefenbaker) "austerity programme." It made the "decade of darkness" look positively bright. Anyway, the financial problems were coupled with rampant inflation in the cost of burgeoning new technologies (in every service) and a growing public dissatisfaction with the high levels of peacetime defence spending authorized by St Laurent and continued, relatively, by Diefenbaker and Pearson.
There was, also, a "we support the troops when we're needing them, not when we're just feeding them" feeling about in the country, especially amongst the World War II veterans who were, by then (1960-70), in positions of influence and authority in government and industry.
The defence bureaucracy, intent on building a better educated military, was pushing hard for pay raises; the political centre, under public pressure, would not agree. Military salaries in the late '50s and early '60s were falling father and father behind, making it harder and harder to recruit the people needed - quantitatively and qualitatively.
The 'Hellyer corporal' and the commissioned counterpart the 'instant captain' and their corollaries the CFLs (captain and corporal for life) were the result of a little ill considered bureaucratic sleight of hand that got badly out of hand.
There was a follow-up: 'benchmarking' military occupations with civil service equivalents. That project, which was a real boon to our, military, pay packets, was also ill considered and sloppily implemented.
Good intentions, even the best of intentions in all cases, but second rate staff work - too little analysis of consequences, produced less than optimal results.
Edit: typo