Drafts 1-4  comprised 627 men to be 'boatsmen'  in Royal Navy ships.

The 100 men of Draft 4 were the first of the 'general naval service' volunteers.

Admiralty House Museum holds the photos used by and published in Herb Wells' book, "Under the White Ensign".

Some dates match Nicholson's perfectly. admiraltyhouse@mountpearl.ca Admiralty House Museum Staff:

" I went through the Herb Wells collection and here is what I've got.
Unfortunately, what it contains for dates is when the photos were taken,
not necessarily the dates when the contingents were deployed.
How close together those two dates are, I am uncertain.
They are all large group photos with most of the men wearing suits rather than uniforms,
so my guess would be that the photos were taken a decent
amount of time before the men were officially deployed".

I included the information nonetheless, should it be of any help:

First Naval Draft: November 27, 1939
Second Naval Contingent: January, 1940
Third:
Fourth:
Fifth: March, 1940
Sixth: April 26, 1940
Seventh: May 14, 1940
Eighth: June 8, 1940
Ninth: June, 1940
Tenth: August, 1940
Eleventh: August 27. 1940
Twelfth: October, 1940
Thirteenth: November, 1940
Fourteenth:
Fifteenth: March, 1941
Sixteenth: July, 1941
Seventeenth: September, 1941
Eighteenth: September, 1941