Coins and banknotes of Japanese yen are seen in this illustration picture taken June 16, 2022.
That contrasts with Japan's intervention after the 2011 earthquake and tsunami to quell sharp yen rises, in which authorities announced most interventions.
"With stealth intervention, authorities can give markets the impression they could be stepping in more frequently than they actually have," said Atsushi Takeda, chief economist at Itochu Research Institute.
That means Tokyo will need to rely more on its words - or its silence - rather than reserves to shore up the yen.
You could say stealth intervention may be better than nothing, though it's really just buying time."