In 1900, streetcar service was extended south from Watertown Square to Newton Corner, which served as a transfer point between the Boston Elevated Railway (BERy) and suburban operators.

[2] Watertown Yard formerly served as the terminus of the Green Line A branch, with its heavy maintenance shops eventually handling most work for the remaining trolley routes by the 1950s.

On February 22, 1974, the MBTA began conversion of Watertown Carhouse to a trolleybus and streetcar maintenance facility to replace Bennett.

After the newly arrived Boeing LRVs began failing in the late 1970s, the MBTA was desperate for functional rolling stock.

Watertown Carhouse is now primarily used as a midday layover for buses, as a crew base, and for light maintenance work.