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Thread: RAF 53 Omega 6B/542: DEF-3 Specifications

  1. #1

    Post RAF 53 Omega 6B/542: DEF-3 Specifications

    To assist with my understanding of 1950s-1960s British military wristwatches I have been attempting to determine under which Ministry of Defence (MoD) specifications/standards iconic watches such as the RAF ’53 Omega were supplied.

    Unlike American military wristwatches where the specifications are generally marked on the watch caseback, British military timepieces typically do not have such information indicated. Interestingly, it is difficult to find references to the early MoD specifications in forum discussions, published articles, or books on the subject of British military timepieces.

    An example of an early MoD specification is DEF-3, which was published on 1 September 1951 and was the basis for the supply of General Service (GS) wristwatches to H.M Armed Forces until it was superseded by DEF-3A on 20 October 1959. The following outlines DEF-3 requirements and what I consider to be an example of a GS wristwatch supplied under these specifications – the RAF ’53 Omega.

    DEF-3 Movement Requirements

    The DEF-3 specifications required a 12/13 ligne movement fitted with a fully jewelled lever escapement and not less than 16 jewels. The calibre number was to be stamped or engraved on the barrel bridge. The balance and balance spring were required to be constructed of non-magnetic materials and the balance spring was required to be the over-coil type.

    DEF-3 Dial and Hands Requirements

    Under the DEF-3 specifications the dial was required to be matt black with the hour markings in bold white Arabic numerals and white graduations. The minute circle was to be clearly defined in white. The specification required a luminised radial baton at 12, flanked by spots at the outer end (i.e. outside the minute zone at one minute before and one minute after the baton), and radial batons at 3, 6 and 9. Luminous spots were required at all other numerals. The size of the batons were required to be 2 mm long by 1 mm wide, and the spots 1 mm in diameter. A white broad arrow 2.5 mm in height was required to be placed below the centre of the dial above 6 o'clock. The Trade Name or Trade Mark of the watch manufacturer was required on the dial above the centre.

    The hour and minute hands were required to be of skeleton form and luminised; the second hand was required to be white in colour.

    DEF-3 Case Requirements

    DEF-3 required a “dull” stainless steel case with the caseback to have six equally spaced radial key slots. The securing ring was to be nickel-plated brass. The strap bars were to be hard soldered into position. Key dimensions of the case: 48 mm lug-to-lug; 35.9 mm diameter not including the lugs; 17.5 mm (plus/minis 0.5 mm) inner strap bars (add 4 mm for the outer strap bar measurement); depth of the case was to be 10 mm.

    DEF-3 required the caseback markings to be depth engraved with the Government mark consisting of a broad arrow measuring 6 mm in height, the inter-Service number (5CF 1000) and any other marks of identification which may be required by the Purchasing Authority, as determined in the contract.

    1953 RAF Omega 6B/542

    The 1953 RAF Omega 6B/542 appears to conform to all the key requirements of the DEF-3 specifications (refer to photos below which have been reproduced with the kind permission of The ‘53 RAF Omega had a 17 jewel, 30 mm, 283 calibre movement which featured shock-protection and non-magnetic components.

    The original ’53 Omega (“Thin Arrow”) dial layout, including placement of the luminescent batons and spots also corresponds to the specifications. Note that the original "Thin Arrow" dial had radium luminous material which was subsequently deemed unsafe and consequently the ’53 Omega watches were redialled with safer tritium luminous material (so called “Fat Arrow” dials).

    The ’53 Omega was manufactured with a stainless steel case, and the caseback had six equally spaced radial key slots. Key dimensions for the ’53 Omega are consistent with the DEF-3 specifications, although the case diameter of 37 mm is 1 mm larger than the specification (N.B. the DEF-3 specifications allowed for the dimensions to be within certain tolerances, and moreover, the additional 1 mm may reflect the inclusion/non-inclusion of the stem tube when measuring). The markings on the ’53 Omega was as follows:

    Government Mark in the form of a ‘Broad Arrow’

    NATO Stock Number – as was often the case, the NSN was truncated to simply 6645 101000

    RAF Stores Reference code: 6B/542 (sometimes mistakenly referred to as the specification code)

    Serial number of the watch followed by a slash and the year of issue by the RAF: ####/53 [for a small number of ’53 Omega watches the serial number/year was marked within a recessed oval on the caseback (see photo below), it’s unclear why this variation exists – perhaps a later production run?]

    Note that the early/mid 1950s RAF GS Smiths Deluxe wristwatch also appear to have been supplied under the DEF-3 specification. Like the RAF ’53 Omega, the RAF GS Smiths Deluxe had the caseback marked with Store Reference code 6b/542 (note lower-case “b”) and NSN 6645 101000.

    Note: all photos have been used with the permission of
    Regards, Ken

  2. #2
    Join Date
    Jul 2008
    Perth, WA


    Thanks Ken, nice bit of research.

  3. #3

    Default Def-3


    Thanks for the interesting information. Are there any links to MOD DEF-3 and MOD DEF-3A specifications please?

    Terry Andrews

  4. #4

    Default Def-3-A


    Found a copy of DEF-3-A thanks.


  5. #5
    Join Date
    Mar 2009

    Default RAF Omega 6B

    I'm interested in an Omega that seems authentic except the "0" for the numeral 10 is round & not flat sided. is this a fake? thanks.

  6. #6
    Join Date
    Feb 2007


    Does anyone have a link to the DEF-3 document? I'd like to read it.



  7. #7
    Junior Member
    Join Date
    Jun 2017


    Resurrecting this thread to ask for help obtaining a copy of the MoD DEF-3-A document.

    Please send me a PM if you are able to help.

    I thank you for your time and attention to this request.

  8. #8
    Junior Member
    Join Date
    Feb 2008


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