Outstanding review! Perhaps the best out there. Some reviews of this watch have been marred by authors who own a TR-900 but have little or no hands-on knowledge of Blancpains. Your review brings a depth of knowledge that is outstanding.
A couple points. First, there is known a Blancpain FF (not a Milspec) with an original hacking movement. I owned it at one time, and it has been speculated that there was some military connection to the watch. Such movements seem to be very very rare.
The photo of the Bulova "from the net" was taken by me and is of my watch. (You are very welcome to use it, of course.) There are, to my knowledge, only three known examples of this watch. Mine has a replacement insert and crystal, and is the only one with actual issue markings on the back (UDT 21). The original crystal was a high-domed mineral crystal that was soldered in to the case. I have had the priviledge of being able to study this watch closely, and my history of it can be read here: click here
As for who influenced who, it is quite clear that the Bulova company blatently copied the basic design of the then three or four-year-old Blancpain design. There does not appear to have been a Navy specification, per se, that the Bulova was drawn from, although the Bulova was designated MIL-W-2181. In other words, Bulova probably came up with the design, not the Navy. That being said, at that time there was a very cozy relationship between Bulova and the U.S. Military procurement system.
The Bulova was tested extensively by the Navy, along with the Submariner 6538, the BP FF Milsepc I, among others, and various suggestions were made for improvements of the design. click here for the detailed report (23 meg .pdf download).
In 1959, most of these suggestions were then presumably incorporated in a new spec, MIL-W-22176 (a copy of which has not yet surfaced), and then in 1961, with presumably more revisions, in MIL-W-22176A. The TR-900 is based on this 1961 spec, although the case and bezel design in the final product vary in small ways from the spec drawings. (Specifically, the case profile and width of the bezel insert.) The spec drawings actually more closely resemble the Bulova than the finished TR-900.
So in summary, the Blancpain TR-900 was based on a copy of the Blancpain Fifty Fathoms. Ironic, to say the least.
As for the date that the Blancpain Milspec I appeared, according to the above US Navy report, twelve Milspec I watches were field tested during the H-bomb tests at the Pacific Island Enewetak in May and June of 1958. these watches had hacking movements. Later, another Milspec I, serial #1595, was tested in February 1959, and a replacement, serial #2725 was tested in March 1959.
Therefore, the Blancpain Milspec I was introduced no later than May 1958. We can also roughly date some of these by serial number.
Thanks to James D., who is solely responsible for 99% of the original research on these watches.