Nuns, did you say?

Philly born director William Keighley and great character actor James Flavin of 100s flicks (ie. a 'fast-talking, granite-jawed Irishman' & West Point grad!, see IMDB) both had something in common as their names demonstrate - Irish Catholic heritage, a theatrical ploy (refined to an art form by John Ford, et al) was to play to that religious heritage when circumstances dictated.
So Duke Gifford being the shrewd lad he was, decided to up the ante of not only saving children w/the ecclesiastical bonus of a couple of Nuns (not more preferable, as you imply, just an added +), appealing to Flavin's character, Mick's (OMG, 'Mick'!?) assumed Irish-Catholic heritage.
Those types of 'movie stereotypes' ran rampant throughout most 30s, 40s, 50s and even 60s flicks were considered comical/familiar and not as PC abhorrent as they appear in this secular, homogenous society.
Ironic cause Ford virtually built a classic, tremendous career on those very same theatrical devices (see 'Quiet Man', to name one of many).

GO Nova!

I didn't take it at all the way you did (that nuns were more important) I thought the crew had had to be on their best behavior with children AND nuns onboard. Not sure how long they had to behave, but for a bunch of young men at war in that era, I'm sure they really had to toe the line, meaning "to conform to a rule or a standard".

JMHO...