DOZENS of large black metal trunks lined the hallway of the bandroom at Stanley Fort yesterday, as the Black Watch regimental band played for the last time in front of their battalion. The band has served with the Black Watch for more than 200 years, and Lieutenant-Colonel Sir Andrew Ogilvy-Wedderburn spoke of the ''great sadness'' many felt to see it disbanded. From May 1 the band becomes officially ''non-effective'' and the members will be flying back to Britain during the following weeks. But they will be leaving behind the black trunks, and with them thousands of dollars worth of music. Bandmaster Ian Peaple explained that the music was being given to the Hong Kong Academy for Performing Arts, as part of the ''Music for Millions'' campaign. The idea, he said, was to introduce local children to Western music. ''It's a godsend,'' said Margaret Crawford, the head of the wind, brass, percussion and harp section of the academy. ''The academy has three concert bands, which have only been playing for a few years and building up a collection from scratch is very difficult, time-consuming and expensive.'' The academy has in the past borrowed music from the regimental band of the 1st Battalion Royal Regiment of Wales, and more recently from the Black Watch. The decision to donate such a large part of the collection to the academy was taken because the band will amalgamate with the Scottish Highland and Lowland bands, which already have much of the music. ''Some of this music is 100 years old, and quite a lot of the pieces can't even be bought anymore,'' Warrant Officer Peaple said. ''But it's a legacy that we can leave behind for the people of Hong Kong.' and it marks the close ties we have always enjoyed with the community.''