"24 heavy machine guns" does indeed sound like a very small number for a whole division, especially when you consider that, at the outbreak of war, a German regular army division was a powerful self-contained organisation of around 17,500 men, along with over 4,000 horses. A German division on the march towards war in 1914 had, in addition to its two infantry brigades:

Two field artillery regiments (18 77mm field guns and 6 light howitzers);

One cavalry regiment;

One or two pioneer (field engineer) companies and a divisional bridging train;

One or two medical companies, plus a bearer company and a veterinary detachment;

And in the horsed transport supply train, it had artillery and infantry ammunition columns and even its own bakery.

So, knowing how horrifyingly effective machine guns are in defensive warfare, why were only 24 of them found in such a massive force, just 12 for each entire brigade of infantry? (to be pedantic... there were 30 rather than 24 MGs in total in a 1914 German division, as the cavalry regiment had a further 6 mobile machine guns, although they generally wouldn't be deployed with the infantry).

But before answering that question, it's worth noting that in 1914 the Germans could put three times as many heavy machine guns as the British and French into the fighting line. If we drill down to the level of an infantry battalion (about 1,000 men) and compare a 1914 German battalion with its British and French counterparts, we see a big difference. The MG section of the German battalion was commanded by a hauptmann (captain) and consisted of three sub-units, each with two Maxim MG08 guns and led by a lieutenant. The British MG section, meanwhile, consisted of a just single unit of two Vickers or Maxim guns commanded by a subaltern (junior officer), and the French MG section was similar, with just two Hotchkiss guns.

So that "24" number you quote certainly doesn't seem like a lot, but it's still significantly more than the opposition. And the reason for this apparent lack is really that none of the belligerents went into the war with the intention of fighting the sort of drawn-out siege warfare that developed. The German military arguably went into the conflict better prepared than most in terms of planning and equipment, but there was still no expectation of the static trench fight that was to come. That was 1914: things changed, and rapidly.

Once the trench lines began to form, all nations quickly recognised the critical importance of machine guns in defending them. Our German division in 1914 had 24 heavy guns. The same division in 1918 would have 130 heavy and 216 light machine guns, and this number included specialist marksman machine-gun detachments that had been organised in most divisions by war's end. If we drill down to the battalion level again, each now has 12 heavy MGs (the same as the whole brigade in 1914), plus 24 light 08/15 Maxims spread through the fighting platoons, with many more MGs controlled and deployed at the brigade or divisional level.

So, to come back to your question, the number of "24" heavy machine guns in a German division is a figure for 1914, when commanders were marching their men into a war they expected to develop along more 'traditional' lines, with cavalry dashes and grand flanking manoeuvres, and had little concept of the course it would ultimately take. Jump to 1918, after years of tactical evolution and hard lessons, and that number flies up to 130 along the divisional front, with more than 200 lighter automatics in support.

Main source for the figures is The Western Front Companion edited by Mark Adkin.