I've found many variants of the formal portraits shown below, mostly from World War I. It's impossible to know if their subjects came back, but the fading of this one suggests that it sat in a frame for many years and gradually faded:
(more detail)

Some were taken in case the unthinkable happened:
(more detail)

Somehow very Canadian, very not-American. What is it?
(more detail

Because of all the to-and-fro of migration, quite a few people of Nova Scotian stock served in the American armed forces. Here's a brace of brothers (on the back: John's oldest boy... John's second boy I think it's the one in the Navy Arthur C. Roscoe son of John and Bertha):
(more detail)

Another Doughboy:
(more detail)

For another view of WW I activities, see extracts from a 3-foot panoramic view of the Jordan Marsh Rifle Club's Preparadness Parade, May 27 1916

World War II sparked an avalanche of picture-taking. Some images feature gravity-defying headgear:
(more detail)

Perhaps the hair is the single (triple?) most interesting element. This one is labeled "Elwood, Elwood Jr., and Anne as Elwood was leaving for Guam, May 14 1945":
(more detail)

IWW II also produced a lot of group photographs of military people in lines. These three are details from a Royal Canadian Army Medical Corps group at Petawawa Military Hospital, May 21st 1942:

(more detail)
(more detail)
(more detail)

This one may help to explain why sailors are called 'gobs':
(more detail)
For fuller explanation, consult the third sense at answers.com:

Probably shortening of earlier gobshite, wad of expectorated chewing tobacco, sailor. See gobshite.

...and while we're on the subject, consider all those folksongs about young maidens who dress themselves in sailor's clothing and go to sea, only to be rumbled by Wicked Captains...
(more detail)

From an earlier era, another case of two sons in the Forces (compare the ears...):
(more detail)

The Queen's Own Bellhops:
(more detail)

The Queen's Own Soupstrainers:
(more detail)

...and the Sackbut Corps:
(more detail)

This one memorializes a trip to French Cross, also called Morden, not far from the Greenwood airbase:
(more detail)