Much better copies of the images described in Roger’s posting are embedded in a Youtube film (at about 18 mins 58 secs, and 20 mins 55 secs).

"The Sinking of SS Laurentic (1908)"

In the former, I think you can make out a gun rather than some booms on the foredeck, the latter is --- just a nice picture.
Later, at 29mins 20 secs as mentioned by Roger a diving team took shots and there’s an underwater image of an unshielded gun -but no visual clue where it is installed. (I didn’t have the sound on – so it may well all be explained in the commentary).