Brayton engines were some of the first internal combustion engines which had enough power density that they could be used for motive power. Durring the 1870's several Brayton engines successfully ran in boats and 2 engines were installed in submarines and one was installed in a rail car and another in a bus. Early Otto cycle engines did not have a good power density and were not widely adopted for motive power until the 1890's In 1878 Dugal Clerk obtained a Brayton engine and modified from it from constant pressure cycle to a constant volume cycle by installing a spark plug which allowed him to delay the combustion until after the admission valve had closed. Clerks first 2 stroke engine was very similar to the Brayton of 1872 with the exception of a delayed combustion. In 1880 Clerk made a 2 stroke (Reid type) that compressed the air fuel charge in the power cylinder a second piston moved the charge into the cylinder under slight pressure. Later Baldwin (loop type) would use the back of the power piston to move the air / fuel into the power cylinder. Inventors Nash, Day and Frederick were the first to make ported 2 strokes where the air / fuel would pass through the crankcase.