From the National Security Archive,
Document 72 (PDF file): Telephone conversation transcript, General Hull and Colonel Seaman [sic] – 1325 –13 Aug 45, Top Secret
Which includes:
H[ull]: What General Marshall wants to know is the status of the development of these bombs so we can best determine how to use them. There’s one of them due up the 23rd as I recall it.
S[eaman]: There’s one ready to be shipped – waiting on order right now.
H: If the order is given now, when can it be ready?
S: Thursday would be its readiness; the 19th it would be dropped.
H: In other words, three or four day advance notice before it can be shipped, and six days after that when it can be dropped.
S: That’s figuring it so it will be safe. Then there will be another one the first part of September. Then there are three definite. There is a possibility of a fourth one in September, either the middle or the latter part.
H: Now, how many in October?
S: Probably three in October.
H: That’s three definite, possibly four by the end of September; possibly three more by the end of October; making a total possibility of seven. That is the information I want.
S: So you can figure on three a month with a possibility of a fourth one. If you get the fourth one, you won’t get it next month. That is up to November.
H: The last one, which is a possibility for the end of October, could you count on that for use before the end of October?
S: You have a possibility of seven, with a good chance of using them prior to the 31st of October.
H: They come out approximately at the rate of three a month.
…
S: The biggest gap will be between the one now and the one for the first part of September. After that, I would say approximately one every ten days.
The discussion suggests the use of nukes to support an invasion, with bombs stockpiled in advance and then dropped in mass over a span of a few days.
Fortunately for the Japanese, their Emperor finally grew a pair and surrendered.