I managed to view a scan of a photograph very similar to one you are describing, which was in Vosper MTBs In Action, although there was no specific mention of Alexandria, however, the following point is of relevance to any black & white photo. In general it's notoriously difficult to second guess what colours in a black & white photograph actually are, as I know from having done photography in the past, and scanning and using Photoshop etc, that a photograph is essentially a record of the levels of luminance present, where the highest level in a photograph is shown as pure white (over-exposed) and the very darkest, black (under exposed). On a sunny day, the very brightest points would be the dazzling glints of light on top of the water, and if you exposed for those, the rest of your photograph would be very murky indeed. The next brightest point in a subject like this is going to be the tops of caps, which are bright white in the sunshine, and to capture their shape — that is define their tops from their sides at certain points, rather than their becoming an amorphous white blob on the tops of heads — the exposure setting used, would likely send other shades of white somewhat grey by comparison — again in terms of the levels of luminance as perceived by the camera film. So it is, that sometimes something that is light grey or blue, with the sun on it, such as say the tops of torpedo tubes, can end up having the same level of luminance as say clothing which is known to be white, so in the photograph that I have in mind, the seemingly muddy, grey clothing of the sailors, may very well be white in reality, and my guess, is that they are just wearing whites, even though at first glance, they don't look like they are. Strong sunlight with lots of contrast involved can throw up these seeming visual anomalies. Hope that helps!