I'm relatively familiar with the character and this issue, having read it when I bought it decades ago and a couple of weeks ago when I unearthed it from a box. I re-read it last night and I remember what struck me all those years ago. How did Swift start under the sea, find Atlantis under the earth and then end up staked out in the desert? Prof. Pickering comes over the horizon in the nick of time. A bit odd.
As crash notes, Silver does sfa and I suppose she's there as the glamour.
I was never totally enamoured of the art but still enjoyed the read. Fast, lots of action, quite exciting and a bit violent for British comics in 1949. But, saying that, the cover/1st. page is dynamic and it almost seems as if the art gets clunkier as the story progresses.
This was published when I was 10 and I vaguely remember seeing Boardman comics in Woolworths, but never bought or read them - I don't think my mother would have approved.
Denis McLoughlin was well known as a paperback cover illustrator. You can see examples here:-
https://www.flickr.com/photos/42080330@N03/galleries/72157623940377149/As for 3d, that is the cover price, which for all you non-Brits, is 3 old pence (thruppence) in old money - LSD, before we went to a metric system in the '70's.
No, of course I wasn't 10. I was only born. Senior moment there!