Objectives: To investigate: (i) the chronicity and phasic variability of sleep patterns and restriction in recruits during basic military training (BMT); and (ii) identify subjective sleep quality in young adult recruits prior to entry into BMT. Design: Prospective observational study. Methods: Sleep was monitored using wrist-worn actigraphy in Army recruits (n = 57, 18–43 y) throughout 12-weeks of BMT. The Pittsburgh Sleep Quality Index (PSQI) was completed in the first week of training to provide a subjective estimate of pre-BMT sleep patterns. A mixed-effects model was used to compare week-to-week and training phase (Orientation, Development, Field, Drill) differences for rates of sub-optimal sleep (6–7 h), sleep restriction (≤6 h), and actigraphy recorded sleep measures. Results: Sleep duration was 06:24 ± 00:18h (mean ± SD) during BMT with all recruits experiencing sub-optimal sleep and 42% (n = 24) were sleep restricted for ≥2 consecutive weeks. During Field, sleep duration (06:06 ± 00:36h) and efficiency (71 ± 6%; p < 0.01) were reduced by 15–18 min (minimum - maximum) and 7–8% respectively; whereas, sleep latency (30 ± 15 min), wake after sleep onset (121 ± 23 min), sleep fragmentation index (41 ± 4%) and average awakening length (6.5 ± 1.6 min) were greater than non-Field phases (p < 0.01) by 16–18 min, 28–33 min, 8–10% and 2.5–3 min respectively. Pre-BMT global PSQI score was 5 ± 3, sleep duration and efficiency were 7.4 ± 1.3 h and 88 ± 9% respectively. Sleep schedule was highly variable at pre-BMT (bedtime: 22:34 ± 7:46 h; wake time: 6:59 ± 1:42 h) unlike BMT (2200–0600 h). Conclusions: The chronicity of sub-optimal sleep and sleep restriction is substantial during BMT and increased training demands exacerbate sleep disruption. Exploration of sleep strategies (e.g. napping, night-time routine) are required to mitigate sleep-associated performance detriments and maladaptive outcomes during BMT.