First Phase (Basic Conditioning)
First Phase is the seven-week opening block of BUD/S, the phase that selects and prepares candidates physically and psychologically for the rest of the pipeline. It holds Hell Week, and it is where most of a BUD/S class is lost.
The Three Parts of First Phase
The first three weeks are progressively more intense physical evolutions, building the class toward Hell Week. Week four is Hell Week itself. The last three weeks begin with recovery and rehabilitation after it, then add mentorship sessions, leadership and ethics discussions and academic topics, and bring back testable events as the class recovers. MILPERSMAN 1306-1016 (10 December 2024) counts three test gates in the phase, with Hell Week among them.
What Is Graded
Before Hell Week, a candidate is dropped automatically for failing an evolution with set standards, which the Navy's 2023 command investigation lists as the swims, the runs and the obstacle course; that drop is approved by the commanding officer rather than argued before a board. The class is given daily verbal or written feedback on performance, and a candidate who trends below average across shifts is pulled from training for review. Grading is continuous, not a single day.
Why First Phase Decides Most Classes
Averaged over the classes since 14 November 1998, 66% of a class is lost across First Phase's seven weeks, against about 5% across Second Phase and 3% across Third Phase. The three weeks before Hell Week account for 45% of the starting strength, most of it drop on request, and Hell Week takes another 21% of the candidates who enter it. The two later phases lose very few people, which is why arriving at First Phase able to handle volume matters more than arriving able to handle one hard day.
The three weeks before Hell Week are what the running and swim volume in a preparation plan is for. Arrive able to repeat hard days, not to survive one.
Related Terms
Hell Week is the fourth week of First Phase at BUD/S, the five-and-a-half-day stretch the Navy calls the course's crucible event. A class goes into it after three weeks of increasingly hard physical evolutions and comes out of it either still in the class or gone from the pipeline.
Second Phase is the seven-week diving block of BUD/S, where selected candidates train on open-circuit and closed-circuit diving gear. The instruction for the programme lists physical training, distance running, swimming and the obstacle course alongside the diving itself.
The obstacle course, known at BUD/S as the O-course, is the timed route candidates run repeatedly against set standards. It appears in the orientation course, in Second Phase's course content, and among the graded events of First Phase.
The 1.5-mile run is the final event of the Physical Screening Test (PST) and measures a candidate's running speed and cardiovascular endurance. Performed after the swim and calisthenics events, it tests the ability to produce a fast run effort on fatigued legs, a skill directly relevant to BUD/S demands.
BUD/S (Basic Underwater Demolition/SEAL) preparation refers to the structured physical training undertaken before entering the Navy SEAL selection pipeline. The Naval Special Warfare Physical Training Guide outlines a 26-week progressive program designed to build the endurance, strength, and mental resilience required to attempt BUD/S.
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