Greetings, Andy,
It's important to understand the context of why marching in lockstep, even unintentionally, was such a concern.
This was nearly within living memory of an incident in which just 74 soldiers crossing a bridge just once was enough to destroy said bridge. Now, remembering what Thomas said:
... and playing that out on a daily basis for about a week, you can understand why the shipbuilders were keen on those men breaking step while in the fireman's passage. Especially considering they were trampling right on top of the ship's keel.
Kevin