Episode 75 of The Trigan Empire
aka The Voyage of the Perici
Het slaapmonster (Dutch title)
The Sleep Monster (Dutch title, translated)
Written by Ken Roscoe
Illustrated by Gerry Wood
Submarine Mission was originally published in 6 instalments in issues 878 (11 November 1978) to 883 (16 December 1978) of Look and Learn magazine.
To date it has not been reprinted in English.
Plot summary (Dutch)