The SCL was in need of replacement power for its Bone Valley (near Tampa, Florida) phosphate lines, and GE suggested road slugs for this operation. A MATE differs from ordinary slugs in three ways: their 65,413 to 67,588 pounds of added tractive effort surpasses that of most slugs, they are designed to operate at road speeds (they are equipped with Blomberg trucks with GE 752 traction motors), and they also serve as fuel tenders. Each MATE carries 3250 gallons of fuel that the modified U36B can draw on while under way. These remain the only road slugs constructed by a major builder, but that could change. The first 10 MATE's (originally SCL #3200-3209, later SBD #5200-5209) were single ended, and could only take power from the mother at one end. The second batch (SCL #3210-3224, SBD #5210-5224) are double ended, and can take power from either end, or in a third mode of operation, can be placed between two mothers and draw power from both. The double-ended MATE's have headlights and numberboards at both ends, the single-ended MATE's have a headlight and numberboards at one end only.