In 1961 Burrfish was loaned to the Royal Canadian Navy where she served as HMCS Grilse (SS 71) and was used primarily as a training boat from 1961 until 1969.

During her third war patrol the ship accomplished several special missions, conducting reconnaissance of the beaches of Palau and Yap where landings were planned.

Between February 1950 and June 1956 she completed three tours with the 6th Fleet in the Mediterranean Sea; participated in several major type and inter-type exercises; and operated along the eastern seaboard as a radar picket ship.

The Royal Canadian Navy was interested in reestablishing its submarine service in the late 1950s and as an essential stopgap to further purchases, they sought a boat to train in.

[10][11] Grilse underwent one month of sea trials before transiting to her new homeport at Esquimalt, British Columbia, arriving on 14 July 1961.

[11] As a result, Grilse spent most of her time as "clockwork mice" for surface ships and aircraft, as a passive target for their training.

Maritime Command chose to accept the offer and HMCS Rainbow was purchased as a direct replacement for Grilse on the west coast.

[13] Grilse was also used as a test platform for measuring the nature of turbulence, the results of which were analyzed by scientists that included French polymath Benoit Mandelbrot, whose thinking on fractals was substantially shaped by this experience: "On a visit to Vancouver, I asked to listen to the recordings.

Not possible, I was told; the audio tapes, while playable, spanned too broad a frequency spectrum from high pitch to low, most of them outside human earshot.

But if they had taken the trouble to study the intervals, to analyze the relative proportions of high and low patches, they would have found something else: a turbulent process that proceeds in bursts and pauses, and whose parts scale fractally.

Instead, seen in all three dimensions, it was a complicated pattern of churning eddies and torrents, all interrelated from start of journey to end of journey—in effect, over an infinite span of time and space.