Today in WW II: 13 Jul 1941 British-USSR mutual aid pact signed.  More 
13 Jul 1943 Battle of Kolombangara in the Solomon Islands; US Navy prevents Japanese from landing reinforcements on New Georgia, although Japanese ships escaped and US had 3 seriously damaged.
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Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639)

The Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639) was a specialized tractor for towing ponton trailers loaded with bridge sections. The Mack NJU-1 was powered by the Mack EN532 6 cyl., 136hp engine, with 532 cu. in. displacement. The wheelbase was 148 inches, width 96 in., length 237 in. and height 114 in. The maximum lowed load was 30,000 lbs. The box behind the cab was for stowage of tools and equipment related to bridge erection duties.

See also the very similar Autocar U-8144-T Ponton Tractor.

Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639)
Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639).

1941 photo of Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639)
1941 photo of Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639).

Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639) with ponton trailer
Mack NJU-1 Ponton Tractor, 5-ton, 4x4 (G-639) with ponton trailer.