The basic nature of the W-46374 specification (i.e., inexpensive, non-maintainable, non-hacking, general purpose, etc) was maintained and modestly updated with a series of revisions and amendments spanning twenty-two years from 1964 until 1986 - when the "D' revision came out and completely changed the nature and scope of the MIL-W-46374 spec. A major milestone along this long trail of revisions and amendments was the publication of MIL-W-46374A.
An addendum published in June 1973 changed the metallic case material requirment to "Stainless Steel" from the earlier "Corrosion Resistant Steel". So, from this point until the "B" Revision went back to the "Corrosion Resistant" description, all metallic cases had to be stainless steel. This is the only period in the history of the MIL-W-46374 spec that Stainless Steel was actually required, even though it was commonly used.
Plastic versions were produced by Benrus and Westclox (SEP 1970). The two latest Benrus plastic issues, JUL 1975 (see example above) and JAN 1976, had the H3 and radiation symbol on the dial. This was curious, because the watches were made under the MIL-W-46374A spec which does not mention or require these markings.
The requirement for the H3 and radiation symbol to be on the dial, "centrally located and clearly visible", was first introduced in the MIL-W-46374B spec which was published on 7 May 1975. Why do "A" watches incorporate requirements from the "B" spec?
The contract awards marked on both the JUL 1975 Benrus's I have are dated 1974. The JAN 1976 watches were ordered by the same award, and perhaps amended as well. This timing would certainly allow for such an addendum to be added, and might explain this overlap in specifications and the curious "prescience" of these later Benrus plastic MIL-W-46374A issues. Occasionally, a metal-cased Aussie W-46374A was made, late in the production cycle for these watches, with the same curious addition on the H3 and radiation symbol to the dial. I suspect that the same rationale may apply, as for the Benrus plastic-cased watches, or Hamilton perhaps was just short on the older dials and used these new "B-type" dials to complete their orders for the Aussie versions.
I have been able to positively identify at least two variants of the MIL-W-46374A produced with cases made from stainless steel, or, from corrosion resistant steel. One version was made by Hamilton for the Australian Army, and is shown at the top of the page. Another was made by Hamilton for US Forces (several issues dated from mid-1972 until 1975). This US-Issue version is very similar to the Aussie issue. The only differences being the markings on the caseback, as you would expect, and the fact that the US version has a one-piece case and the Aussie version a screwback case. Images of the Australian Army issue can be seen by clicking on the steel-cased MIL-W-46374A at the top of the page. The US version is shown in the link via the image below.
Caseback Markings: a US-Issue MIL-W-46374A Hamilton
These metal watches were issued in the early 1970's (both the Aussie and US Variants) and they are relatively scarce, much more so than the plastic Benrus versions. Hamilton MIL-W-46374A watches command $120 and up on eBay, even though they are very similar to the ubiquitous MIL-W-46374B Hamiltons that followed. I have heard that there was also a Wittnauer 1970 version of the MIL-W-46374A General Purpose Watch, but have not seen evidence that these Wittanauer's were actually MIL-W-46374A watches.
The plastic Benrus issues have quite a range in value. I have seen minty or Mint in Box versions command more than $200, but typically they sell for $75 or less. Few Westclox MIL-W-46374A plastic watches show up for sale or auction, but a good one should command a high price from a motivated collector. This is particularly true of Westclox W46374A watches marked as "WESTCLOX NO. 75092". According to Whitney, these may contain a Seiko 17 j movement which is much more reliable than the more common Japanese D-407 7 j movement found in other Westclox models of the W46374A and in many 79092 examples as well. These 17J models are rare and may command $150 and up at auction. Unfortunately there is no way to tell if the 17 j movement is on board short of opening the case.