The accusation made by several prominent policymakers in the interwar period that so-called "Merchants of Death" convinced Congress or Woodrow Wilson to intervene in the First World War proved inaccurate, although it did bear influence on the isolationist tendencies of the 1930s. American perceptions of the world, which were severely altered by the Second World War, played the key role in the jump from isolationism in the 1930s to interventionism and collaboration in the postwar world.

Like you say, there were some who accused arms producers of having tricked the United States into going to war in 1917. After the rise of Hitler in the early 1930s, this became a focal point in American discourse about global politics. The United States Senate, of course, had rejected the Treaty of Versailles after the First World War, and so the United States held no international obligation to aid in the mutual defense of Europe. Therefore the United States maintained the right to choose whether it became involved in European affairs again (or so it seemed to people at the time). It was in this atmosphere of rising tensions in Europe that two influential books were published that both accused the arms industry of having tricked Wilson into going to war: Merchants of Death (1934) and War is a Racket (1935). This pervasive American assumption that the arms industry, which did benefit from the war, had tricked the United States government culminated in the Senate's "Nye Committee," a committee led by Senator Gerald Nye, who hoped to nationalize the American arms market.

Ironically, the scathing conclusions reached by the Nye Committee are often cited by historians as proof that the "Merchants of Death" did not in fact influence the United States to go to war in 1917. With the power of the Senate behind him, Nye could only find scant evidence of any connection between the arms industry and American decision-making at the time. Shipbuilders had lobbied Congress to increase the size of the Navy, sure, but as /u/DBHT14 notes, their influence did not outlast the war. Moreover, while Nye found that, generally speaking, "that there is no record of any munitions company aiding any proposals for limitation of armaments, but that, on the contrary, there is a record of their active opposition by some to almost all such proposals," this is to be expected and hardly represents the kind of "smoking gun" that Nye had hoped to find when he started his investigation. That the arms industry general lobbied for, and not against, the government's procurement of arms is not much of a revelation. It should be noted that the committee's final report cited here did accuse the arms lobby of "bribery," but it fails to name a specific example of this. If a Senate committee led by a man determined to uncover an arms-industry conspiracy could find no evidence of such a conspiracy, then we can assume that none likely existed.

Nevertheless, the concept of the "Merchants of Death" strongly influenced American policy at the time, with the first of the so-called "Neutrality Acts" passing before the Nye Committee issued its final report. With an eye to the heavy amount of trading that the United States did with England and France prior to American entry into the war, Congress passed a series of acts that barred American companies from trading with any belligerent nation (that is, a nation at war), whether they were an American ally or not. The American population supported these acts; the president of the United States at the time, Franklin Roosevelt, did not. Indeed, Roosevelt moved to include loopholes in the bills, which Congress eventually rejected. In 1937, Roosevelt gave his famous "Quarantine Speech" in isolationist-leaning Chicago, in which he called for the United States to quarantine aggressor nations through economic policy, but his speech did not sway Congress. When the Second World War began in Europe, Roosevelt had no legal way to send arms to what he perceived to be America's greatest ally in the war, Great Britain.

After Germany conquered France in 1940 and Great Britain looked to be Hitler's next target, American sentiment shifted. In March of 1941, Congress passed the historic "Lend-Lease Act," which allowed Roosevelt to "lend" arms to Great Britain with the understanding that Great Britain would "lease" military bases to the United States after the war and pay for any arms that it could not return. If this sounds absurd, it is: it was a legal loophole that allowed the United States to sell arms to Great Britain in exchange for favors after the war. During this same year, Roosevelt proved able to now implement the full range of his "quarantine policy" that he had pitched four years earlier, as he implemented an oil embargo in Japan as well. Japan, which had been militarily involved in China for years, still had not yet obtained the oil fields necessary to continue its war, and so this embargo represented a devastating blow to Japan's imperial ambitions.

American sentiment had shifted away from isolation and towards intervention over the course of 1941; by the end of the year, the Japanese attack on Pearl Harbor would change American perceptions permanently. To fully understand the meaning of this change, we need to take a step back to 1938, before the war, when Hitler had demanded that the ethnically German portions of Czechoslovakia be ceded to him. France and Britain, with the clandestine support of Roosevelt, had agreed to revoke France's alliance with Czechoslovakia and hand over this area to Germany at the Munich Conference of September, 1938 (Hitler infamously violated the agreement in March of 1939 by occupying the rest of Czechoslovakia). At the time, Americans had perceived this as a strictly European affair, i.e., one that the United States could remain uninvolved in if it so chose. After the attack on Pearl Harbor, however, Americans came to understand that the Atlantic and Pacific Oceans did not protect the United States from world events. A so-called "Munich Syndrome" influence American policymakers thereafter, which informed them that any powerful aggressor could not be appeased and would come into conflict with American interests. Pearl Harbor drove home the idea not only that aggressors would come into conflict with American interests, but, given modern technology, could launch attacks on the United States itself. Witness to an attack on an American naval base, the general population embraced the idea that the United States was inevitably involved in world events.

This radical change in perception greatly served Roosevelt, who had opposed isolationism even before the war. Before the war ended, Roosevelt oversaw the creation of the permanent United Nations, which he perceived to correct the error made by the United States after the First World War when it did not join the League of Nations, and he presided over the creation of the "Bretton Woods" financial system, which would guide global finance of the Western world for decades after the Second World War. Roosevelt hoped to maintain the Soviet-American-British alliance in the postwar world, and these three nations, along with France and China, Roosevelt envisioned would be the guarantors of global peace. Of course, the rising Cold War ruined Roosevelt's vision after he died, and the United States and the Soviet Union became locked in the Cold War. Nonetheless, the United States could not return to its policy of isolationism that it had promoted in the 1930s--every single American president from 1945 through the end of the Cold War believed that the United States had to "contain" the Soviet Union by challenging the Soviets anywhere they might gain influence in the world. The age of nuclear missiles erased any notion of global isolation that existed prior to the Second World War, which Americans understood to have been an illusion regardless.

I can offer piece of evidence about the lobbying power of the arms industry after 1918 or the lack thereof.

Because precisely in your time frame we have one of the largest and most pervasive arms control schemes ever attempted.

That is the "Battleship Holiday" and the associated Washington and London Naval Treaties.

The treaties, adhered to by the US, UK, France, Japan, and Italy, stopped capital ship construction for most of a decade and curtailed the size of the great fleets of the world. This put a stop to the massive USN envisioned under the 1916, and 1919 Bills, while the 1920 election returned to a distaste for huge budgetary items and such a large battlefleet, though the one already built and building was sufficient to be on something approaching parity with the RN. While Britain was doing all she could to avoid another dangerously expensive arms race. And Japan was split between those committed to the 8-8 Fleet and those willing(including a younger Yamamoto) who were willing to deal.

Thus the US agreeing to the treaty stopped several whole classes of ships being constructed, limited others, and in general was a large hit to naval yards which at the time were about split between directly Navy owned and private, and who had done much expansion in the build up of the USN in the previous decade.

In the space of about 3 years to USN went from building 4-5 capital ships at any one time, to yards finishing up their paltry orders of destroyers and then having to look elsewhere for work. And the armament, armor, and machinery builders the same.

So we can at least say that the Defense Industry was not powerful enough in the 20's to stop the great navies of the world from essentially putting a halt to major construction for most of a decade.