Co-ordinated intervention by US and Japanese authorities aimed to prop up the yen. While the exact amount of US financial firepower deployed is unknown, analysts estimate Japanese authorities bought around ¥8.45tn ($52.8bn). The US move followed a Japanese currency intervention and rate checks by the New York Fed.

Despite the symbolic significance of US involvement, the quantity of currency they likely purchased is estimated to be less. US foreign exchange assets are split between the Treasury's Exchange Stabilization Fund (ESF) and the Fed's System Open Market Account (SOMA), each with $19.1bn in FX assets. Liquidating all euro holdings in both could yield a maximum trade ticket of approximately $26.3bn.

However, US authorities may have used currency forwards, potentially allowing for much larger trade sizes, limited only by counterparty risk from banks like Goldman Sachs and Morgan Stanley. The exact figures will be revealed by the US Treasury on August 30.