Abstract Introduction Sleep quality is known to be negatively impacted during military operations at sea. Yet, there are limited naval studies that explore measures of sleep disturbances and sleep-related impairment, especially in relation to different warship classes. This analysis compares sleep disturbances and sleep-related impairment across two warship classes during similar at-sea periods. Methods 432 sailors (77.6% male; 27.4±7.1 years) participated in a training evolution aboard either a destroyer (DDG; n=194) or an amphibious class ship (LHD; n=238). Participants completed a 7-day recall questionnaire assessing their sleep and health behavior prior to getting underway (baseline) and 1–2 days prior to completing a 2-week underway (underway). Primary outcomes included the PROMIS Sleep-Related Impairment scale (P-SRI) and the PROMIS Sleep Disturbance scale (P-SD). While underway, participants self-reported their diet quality, daily caffeine and nicotine intake, overall health, and daily time spent exercising; these factors were included as covariates in all analyses. Linear mixed effects models were used to explore the within-subject effect of baseline vs. underway sleep and a between-subjects effect by ship class (i.e., DDG or LHD). Independent t tests and chi-square tests were used to compare ship groups at baseline. Results Participants within ship class had a similar age, time in military service, and sex (p≥.06). Across both ship classes, there were increases in severity of sleep-related daytime impairment and sleep disturbances between baseline and underway (P-SRI: B=5.2±0.6; P-SD: B=3.4±0.5; p<.001). Additionally, DDG participants had a significantly greater increase in sleep-related impairment between baseline and underway compared with their LHD-class counterparts (Group*Time interaction effect: B=4.3±0.9, p<.001; LHD: 54.5±0.6 [baseline] vs. 54.5±0.5 [underway], DDG: 54.9±0.6 [baseline] vs. 60.2±0.6 [underway]). Conclusion These results suggest sleep-related impairment and sleep disturbances are greater while underway compared with an in-port environment. Although preliminary, these results suggest that differential impacts on sleep-related impairment may occur across ship classes, even when undergoing similar underway events. Further research is needed to understand how insufficient sleep and its consequences change in shipboard environments and how these effects may vary between ship classes so as to better inform targeted naval-focused sleep health improvement strategies. Support (If Any) Military Operational Medicine Research Program under work unit no. N2010.