Purely scientific. Most closely resembling an M4, but without a viewfinder or rangefinder, the MDa was produced for use in conjunction with a microscope or Visoflex reflex attachment. Introduced in 1966, it has a rapid film loading system and an M4-style rewind lever.
The Swiss firm Alos AG which had been modifying Leicas since 1933 to use in making photographic records of telephone charge dials, found the MDas well suited for their purposes due to their lower cost and absence of a viewing housing. In 1977 the MDa was discontinued and replaced by the MD-2.