Liberty Ships have five, two-level cargo holds that are accessed via their five hatches and feature prominently along the main deck. They provide access to load cargo into the holds below. Multiple wooden hatch covers form the roof of every cargo hold.
A canvas covering is placed over the hatches and held in position with wooden wedges along the perimeter to keep the elements out. They are then secured with metal straps called battens. During wartime, this created a large, yet removable, secure cover for the holds and their precious cargo below. This is how the saying "batten down the hatches” came to be.
The corners at the hatch openings of Numbers Two, Three, and Four Holds were eventually modified. Due to concentrations of high stress inherent in ninety-degree angles, these holds closest amidships were identified as the primary point where cracks could potentially develop. The O’Brien and many other Liberty Ships were retrofitted with stress relievers to prevent cracking. They rounded off the hatch corners and distributed the stress over a larger area. Curved steel plates welded into each hatch corner can be viewed by looking up while visiting No. 2 Hold.
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Immediately forward of No. 3 Cargo Hatch are a standard set of winches for assisting in the loading and unloading of cargo.