For instruction in the use of slide rules, please visit this page covering the Mk IV Slide Rule.  They are covered in the Small Arms Training manuals.


Mk. 1

  • Cat No. C1/BD 2562, List of changes A 9393, RULES, SLIDE, M.G., Mk. 1 – With cord and bead; for use with Mk. 1 Vickers .303-in. M.G. and Mk. 7 ammn.

Is ivory-faced, approximately 11-inch long by 2-in. wide. This has now been superceded by the Mk. III pattern (1940).

The example in the VMGCRA collection is manufactured by B.J.H. & Co Ltd. and dated 1928. It is in its web and canvas case.

It would appear the a more robust metal version of the Rule, Slide, MG, was also manufactured. The example in the VMGCRA collection is dated 1937 and manufactured by Stanley of London. Other than its material, it is otherwise exactly the same.


Mk. I (Aust)

The Australian variant of the Mark I is actually an adaptation of the Mark III that was manufactured in metal following a request from the 2/2nd (Australian) Machine Gun Battalion as they found the wooden Mark III to be unsuitable for jungle warfare.

Their war diary read:

RULES, SLIDE: Probably one of the most useful items of equipment held by Machine Gunners is the Slide Rule. The present issue Rule, slide MG Mk III – .303 VMG for Mk VII amn is quite unserviceable, being made of cane and glued at the joins. The cane swells in the moist climate, the slides will not run freely, the glue gives way at the joints – and the whole thing falls to pieces. should any of these things fail to happen, the white ants make sure that the Rule is u/s. So that throughout all the recent ops we have been denied the use of this most useful instrument.

The Mk IV slide rule, designed for use with Mk VIIIz amn, is of metal construction throughout, and is most efficient. Were it possible to have a similar Rule, suitable for use with Mk VII amn, it would be of the greatest assistance.

It’s interesting to note that they produced the Mark I (Aust) slide rule, rather than make the Mark II (see below) available.

The example in the VMGCRA collection is manufactured by W.H.H. and is in its Australian-made web case, which includes ‘C’ clips on the rear as well as a shoulder strap. It also uses a quick-release tab closure rather than poppers.


Mk. 2

The Mk. II rule, made of duralumin and similar in design to the Mk. III pattern, is special to the requirements of India.


Mk. 3

  • Cat No. C1/BD 2564, List of changes A 9393, RULES, SLIDE, M.G., Mk. 3 – With cord and bead; for use with Mk. 1 Vickers .303-in. M.G. and Mk. 7 ammn.

Is of boxwood, approximately 6-in. long by 3-in. wide, with 2 slides. A cord 24-in. long, having a bead at the free end, is attached to the rule for the purposes of graticulation.

A smaller compact model of the Rule, Slide, MG, that has two slide elements rather than one, this making more calculations possible using the rule.

The example in the VMGCRA collection was manufactured by W.H.H. in 1940. It is shown with the leather case that has a belt loop suitable for the 1903 pattern leather equipment. There was also a web version of the pouch (the example shown manufactured by MECO in 1939) that also had a belt loop for the 1937 and 1940 pattern web equipment.


Mk. 4

  • Cat No. C1/BD 2565, List of changes B4265, RULES, SLIDE, M.G., Mk. IV – With cord and bead. For use with Mk. VIII ammunition

The final version of the slide rule used with the Vickers was the Mark IV. This was the only version suitable for Mark VIIIz .303-inch ammunition. It had two reversible slides for all the possible calculations.

The VMGCRA collection contains several examples from different dates and manufacturers.

They include:

  • Alumilite, 1941
  • Alumilite, 1942
  • R E Co Ltd, 1944
  • B E N Co Ltd, 1967

The Mark IV was carried in a web case with a belt loop fixed with a popper and a thin shoulder strap.


Cases

  • Cat No. C1/BD 0161, List of changes A 1325, CASES, RULE, SLIDE, M.G., Mk. 1 – With web shoulder strap; for Rule, slide, M.G., Mk. 1
  • Cat No. C1/BD 0162, List of changes A 9393, CASES, RULE, SLIDE, M.G., Mk. 2 – With web shoulder strap; for Rule, slide, M.G., Mk. 1
    For carriage of the Mk. I rule, is of webbing with a web shoulder strap.
  • Cat No. C1/BD 0163, List of changes A 9393, CASES, RULE, SLIDE, M.G., Mk. 3, No. 1 – For cavalry

No. 1 (leather) and No. 2 (web), for carriage of the Mk. III rule, are attached respectively to cavalry or infantry equipment.

  • Cat No. C1/BD 0164, List of changes A 9393, CASES, RULE, SLIDE, M.G., Mk. 3, No. 2 – For infantry

No. 1 (leather) and No. 2 (web), for carriage of the Mk. III rule, are attached respectively to cavalry or infantry equipment.

Whilst not officially a variant of the No. 2 case, the Australian slide rule was carried in a case of the same size, fitted with ‘C’ clips and a shoulder strap, as well as a quick-release tab closure.

267-RF-5

  • Cat No. C1/BD 6202, CASES, RULE, SLIDE, M.G., Mk. 4 – For Rule, slide, M.G., Mk. 4

The Mark 4 slide rule was carried in the Mark 4 case, with a strap or using the belt loop / flap that was secured by a popper so it could be removed from behind pouches already on the belt.


Sources:

  • Australian War Memorial, Item 8/5/2, 2/2 Machine Gun Battalion, January 1945, Appendices.
  • War Office, 1940a; 1944c; 1949a
  • Specific source references can be provided if required.