Japan's government carried out large-scale foreign-exchange intervention over three days last summer to slow the yen's decline.

Japan's Ministry of Finance said in foreign-exchange intervention data released on Nov. 9 that it bought yen by deploying a total of 15.4 trillion yen, or about $97.4 billion, over the three days beginning July 30. It was the largest monthly yen-buying intervention on record.

According to Bloomberg, the Japanese government spent 7.98 trillion yen, or about $50.4 billion, on July 30 alone, setting a daily record. It then used an additional 5.55 trillion yen and 1.87 trillion yen over the next two days. Markets had initially estimated that intervention took place over two days, but the data showed Japan stepped in for three consecutive days.

On July 31, the US and Japan jointly bought yen for the first time in about 28 years, since 1998. At the time, US Treasury Secretary Scott Bessent and Japanese Finance Minister Satsuki Katayama said the move was aimed at responding to disorderly currency swings. The two countries also indicated they could intervene again if necessary.

The joint intervention helped push the yen higher. After the operation, the currency broke out of its weakening trend and rose to 152.89 per dollar in early September. It later gave back part of those gains and traded around 158.30 per dollar in Tokyo on Nov. 9.

The data also showed Japan intervened on its own on July 30, one day before the Bank of Japan's monetary policy decision. That differed from its previous practice of entering the market after major economic data releases or BOJ policy decisions. Market participants say Japanese authorities appeared to have chosen an unexpected moment to counter speculative trading.

How Japan secured the dollar liquidity needed for the intervention has also drawn attention. There was speculation at the time that Japan may have sold some overseas securities, including US Treasuries. But after the joint intervention, the two countries confirmed that Japan could use the Federal Reserve's Foreign and International Monetary Authorities repo facility to obtain dollars without directly selling Treasuries.

The Japanese government has also left open the possibility of further intervention. Katayama said authorities' stance on responding to sharp exchange-rate moves had not changed and that they were ready to take bold action if needed. US President Donald Trump and Japanese Prime Minister Sanae Takaichi also expressed concern about yen weakness at a summit in September.