to reduce the width of the tank for rail transportation, where previous models had required partial disassembly to fit within the loading gauge. Rails on the roof carried an unditching beam whose purpose was to help extricate the tank from difficult trenches by attaching it to the tracks. A total of 1,220 were built: 420 males, 595 females and 205 tank tenders, which were supply tanks. The Mark IVs were used successfully at the Messines Ridge in June 1917, where they outpaced the infantry on dry ground, but in the Third Ypres of July and August they found the swampy ground difficult and were of little use. About 432 Mark IV tanks were used during the Battle of Cambrai in November 1917. The first tank-to-tank battle was between Mk IV tanks and German A7Vs in the Second Battle of Villers-Bretonneux in April 1918. Mark V series The Mark V was first intended to be a completely new design of tank, of which a wooden mock-up had been finished. However, when the new engine and transmission originally destined for the Mark IV became available in December 1917, the first, more advanced Mark V design was abandoned for fear of disrupting the production run. The designation "Mark V" was switched to an improved version of the Mark IV, not equipped with the new systems. The original design of the Mark IV was to be a large improvement on the Mark III but had been scaled back to be a mild improvement because of technical delays. The Mark V thus turned out very similar to the original design of the Mark IV – i.e. a greatly modified Mark III. Four hundred were built, two hundred each of Males and Females. Several were converted to Hermaphrodites (also known as "Composites") by fitting one male and one female sponson so that each tank had a 6-pounder. This measure was intended to ensure that female tanks would not be outgunned when faced with captured British male tanks in German use or the Germans' own A7V. The Mark V was first used in the Battle of Hamel on 4 July 1918, when 60 tanks contributed to a successful assault on the German lines by Australian units. It took part in eight further major engagements during the War. A number saw service in the Allied intervention in the Russian Civil War on the White Russian side. Most were