The US suspended convertibility during the civil war and then fought the resulting inflation by reintroducing it later (see https://en.wikipedia.org/wiki/History_of_monetary_policy_in_...)

European nations dropped the gold standard during WW1 and then mostly returned to the gold standard afterward[2]:

"During World War I, most major countries abandoned the gold standard in order to use fiat currency to fund the war effort. As a result, those nations experienced high rates of inflation. The desire to bring inflation under control and restore monetary stability led most countries to plan on returning to the gold standard at some point after the war. Unfortunately, many of the international monetary difficulties of the late 1920s can be traced to decisions regarding the resumption of the gold standard in the mid-1920s. "

There is an interesting history here[1]:

"Britain had left the gold standard in 1914 and responded by increasing the supply of money to stimulate the economy. Production was limited due to substantial decreases in working hours agreed at the end of the war. In 1919 increased consumer demand caused inflation and a price boom.

By early 1920 the Government was more concerned with a desire to return to the gold standard and with the high rates of inflation than with unemployment. In December 1919 the Cunliffe Committee on Currency and Foreign Exchange Rates recommended an early return to the gold standard. The overall objective was to restore pre-war British predominance in international trade, which depended on stabilising the value of sterling around the pre-war dollar exchange rate. This required equilibrium in the balance of payments and the reduction of the money in circulation..."

[1] https://www.nationalarchives.gov.uk/cabinetpapers/themes/eco...

[2] https://cpb-us-e1.wpmucdn.com/sites.dartmouth.edu/dist/c/199...