Sir, what was the role of Pioneers versus that of Sappers in that time period?
In the early days and at the time of my regiment's raising in 1857. The Pioneers and Sappers tasks dovetailed into each other as they mean the same thing. They were combat engineers. They built roads, prepared defences, bridging, demolition and laying of mines.
Later their tasks started to change. Pioneers specialised in road making, construction of bridges etc and the sappers specialised in demolition, mine laying etc. After 1933 the Pioneer and Sapper units were disbanded and merged into the Corps of Engineers. So many elements of my regiment formed part of the Bombay Engineering Group. The Engr Regt in the Indian Army still follows the old system of the British Days. The Bengal, Madras and Bombay Presidencies - The Bengal, Madras and Bombay Engineers.
My regiment came into being, because the then existing 3 Pioneer regiments also functioned as infantry troops and gave a good account of themselves in the Afghan Wars, Wars in China and WWI. The regiment was re-raised in 1941 as an infantry unit and the seniority and battle honours of the old pioneer units (that merged into Bombay Engr Gp) were transferred to the newly raised infantry regiment. The regiment was called Mazhabi and Ramdasia Sikh Regiment before being re-named the Sikh Light Infantry in 1944.