Materials Technology Laboratory
The Materials Technology Laboratory (MTL) was a research facility under the U.S. Army Materiel Command that specialized in metallurgy and materials science and engineering for ordnance and other military purposes. Located in Watertown, Massachusetts, MTL was originally known as the Watertown Arsenal Laboratories (WAL) and represented one of many laboratory buildings erected at Watertown Arsenal.
Source: Wikipedia — Materials Technology Laboratory (CC BY-SA 4.0)