Had a look at the index for that issue on line and it may not be the right one,
U-class Submarines - Proving plans for Ursula, Undine and Unity
i think that mag may be one for a sub , might be wrong but until i can have a look at the article !! .
I will have a look in our archives and see if we have that copy.
daz
Howard it could be one of yours as its only a plan lol.