The A4D-2N was originally delivered with a large radome. The A4D-1 and A4D-2 did not have radar.
Note that "Do Not Paint" is marked on it.
This was subsequently changed to a nose with a smaller radome, which was retrofitted. See picture of what is almost certainly a replacement nose with the smaller radome area in white, although it is usually dark. It is similar to the A-4E (A4D-5) nose in configuration but not lengthened.
And finally, a picture, courtesy Rick Morgan, of a mix of radomes, indicating the original radome was in use through at least 1965.
That helps suggest when the change was made; although it would be nice to know if the new radome was introduced in A4D-2N production, which ended in 1962. The A4D-5's first flight was July 1961. The highest BuNo I have seen a picture of with the large radome is 149574, which was probably delivered at FEB 1962.
The other question is why? I've considered weight reduction, maintenance access, and durability improvement. There are hints of the latter in a Douglas Product Support letter.
Does anybody have any documentation? Or seen pictures of a higher BuNo with the big radome?
Webmaster's Note: If you have any information to contribute please contact the firstname.lastname@example.org