Thanks David for correcting my mistake. All in all we have not yet come very far. Perhaps Mr. Woody can tell us more, as he seems to be selling the photo on Ebay. Does he have the copyright?

IMO 5914252 is a typo.
Yard 556 (PIONEER MOON) - IMO 5278951
Yard 557 (AMERICAN CHALLENGER) - IMO 5014252

When LR first introduced their 6-digit unique numbers in 1964, they added a "5" to the beginning of the sequential number for all ships in the 1963 register. New additions from 1964 were given 64xxxx numbers. The allocation system changed a few times subsequently, but new 5xxxxx were not issued. Thus LR/IMO numbers 5xxxxxx have no relevance to the age of the vessel, except that they were listed in 1963 LR.

Pieter I'm a little confused with reference to IMO 5914252 .. I can't find one. Question .. is it often the case that a later IMO number from same yard is first completed? In this case 527 .. was completed before 501.. which would make 501 the second completed 3 months later.

Photo is also on eBay

https://i.ebayimg.com/images/g/iBAAAOSwPPxeDHgA/s-l1600.jpg

Is this the first American Challenger of 1962, (imo number 5278951)the one that was renamed Pioneer Moon already during 1962, just before the second American Challenger (imo number 5914252) was delivered, a name she kept for the rest of her life? Both were built by Newport News, as yard number 556 and 557 respectively. In your picture her funnel is lacking the little additional set-up, that is visible in the shots I have seen of Pioneer Moon, and also visible on the other shot here of the A Challenger. Perhaps an afterthought but the lack of this little piece in your photo could well support your suggestion that this is the first ship of the series, perhaps on trials. Would be a pretty rare photo if that was the case.