High-speed boat operators (HSBO) are exposed to high-impact forces and unstable platforms that are linked to spine pain and musculoskeletal injury risk. This study sought to determine the effects of different military occupational specialties (MOS) on spine kinematics in 86 active-duty personnel (64 HSBO and 22 Marines). The relationships between spine postures, pain, and disability were also examined. Upright MRI scans were performed in sitting and standing positions to determine sagittal cobb angle, angle with respect to the horizontal plane, sacral slope, T1 slope, and intervertebral angles of the lumbar and cervical spine. Disability and pain were assessed with the Oswestry Disability Index (ODI), Neck Disability Index (NDI), and a Visual Analog Scale (VAS). A two-way repeated measures ANOVA analyzed the effects of MOS and position on spine kinematics, and a stepwise linear regression analyzed the influence of pain and disability. Main effects of position were found for lumbar sagittal cobb angle, sacral slope, and intervertebral angles from L2-S1 (p <​ 0.0001), and cervical sagittal cobb angle (p = 0.02). MOS significantly affected sagittal cobb angle (p = 0.05) and angle w.r.t horizontal (p <​ 0.0001). Neck disability explained 4 % of the variance in cervical cobb angle, T1 slope, and the intervertebral angle at C5-C6. Pain did not predict lumbar or cervical spine posture. Position has a significant impact on spine kinematics in all groups, with MOS-related differences in cervical spine posture. Subjective pain measures did not reliably predict spine posture, underscoring the necessity for objective diagnostic approaches and targeted interventions to mitigate injury risk in HSBO.