It's difficult to answer this question because there was almost no technological 'advancement', in the modern sense, in the periods relevant to your question. Yes, of course there were changes, but they came about very slowly, almost over generations, so the idea of a dedicated body constantly looking to improve and invent weapons is incompatible with the mindset of the time.

It's only in the last 200 years, even less, that an army could rely on having an assurred supply of basic materials, allowing time and resources for thinking about improvements. And only in recent times there was an industrial base to put any such idea into metal and wood.

However, even in this time procurement was handled very differently. Only through the period 1914-1945 were the military themselves relieved of the burden of inventing and improving weapons, and this role taken over by private companies (in the West). Many weapons the British and Americans used in World War Two were still the product of government armouries, designed by government employees.

Before 1945, although private companies were happy to take wartime contracts and there were a few large companies (such as Vickers) specialising in weapons, the private sector knew peacetime would bring an abrupt end to contracts so even companies such as Rolls Royce and Curtiss remained 'civilian' companies. Much of weapons procurement between the wars for Western nations centred on putting out small contracts designed purely to keep some weapons design expertise in existence.

After 1945, the onset of the Cold War and the wealth and newly-found overseas interests of the US saw a much more militarised commercial sector (it's not a coincidence that it was the end of the 1950s when Eisenhower first coined the term 'military-industrial complex'). For a time there was a sort of 'managed conflict' between the government and military branches procuring, and the companies who received the funds and the contracts. This was especially so in the 1950s as technology advanced very rapidly and what the military saw as its needs could also change fast, even for a single project.

Today the development of advanced weapons (there are of course many cheaper, less glamorous and less publicised developments) takes so many years that a company has to be given a contract lasting years with the contract waypoints kept vague, and negotiated as the project unfolds.