In naval tradition, ships and ports may expend gunpowder saluting each other, thus proving their respect and nonaggression. The respect so shown appears greater when more guns are shot off. A common pattern is that one party fires 7, 14, or 21 guns, which are answered equally by the other.
During Japan's period of isolation, the Dutch were restricted to the tiny island of Deshima and scrupulously deferent to their hosts. According to George Lensen's The Russian Push Toward Japan (pp. 148):
... the Dutch ships expected to leave their anchorage and, as was their custom, would salute the imperial fortress.... When the Dutch vessels duly departed from Deshima the following day, they saluted with a hundred and fifty guns each.... The Japanese did not return the salute.
150 guns with no response is very different from the other pattern, perhaps reflecting the unusual relationship those two powers were in. Did similarly disproportionate salutes happen anywhere else?