‘All who were numbered of the camp of Reuben were a hundred thousand and fifty and one thousand and four hundred and fifty, according to their hosts. And they shall set forth second.'
The total force in the camp of Reuben was 150 'lph (families/military leaders) with 14 ‘hundreds' or military units and a special force of ‘fifty'. The special mention of the latter only the once may suggest that they were seen as especially valuable, or alternately that they represented the friendly aliens. They could possibly have been expert ‘slingers'. But it may simply be that the ‘fifty' was added as signifying 5x10, the covenant number intensified, added to the tribe of Gad in the camp of the firstborn, thus indicating that all were within the covenant (a fifty was required if the number of 603,550 was to be obtained). Compare how a ‘thirty' is added in the second numbering, in that case only to Reuben, while both a ‘fifty' and a ‘thirty' are added to the Levites (Numbers 4:36; Numbers 4:40). This is surely not merely coincidental.
These were to be the next to march after the camp of Judah, moving from their protective position on the south side of the Dwellingplace.