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The Deep Autonomous Profiler (DAP) is a full-ocean-depth profiler rated to 11 km. Its hydrographic profiles and water samples can provide information on physical oceanographic properties, seawater composition, and biological communities at every depth in the ocean. Designed around a 24-bottle rosette, the DAP is an untethered system able to autonomously collect temperature, salinity, and oxygen profiles, as well as water samples. An adaptive sampling method was developed to analyze the water-column data to identify and sample desired features while under way. Acoustic ranging-only tracking is used to monitor and geolocate the system underwater. In September 2018 the vehicle was tested to 8377 m in the Puerto Rico Trench. The DAP was able to generate full-ocean-depth profiles and collect water samples at both preset and adaptively determined depths. To demonstrate the utility of the DAP, we radiocarbon dated the deepest water sampled in the Puerto Rico Trench, providing the first direct evidence of hadal water-mass age in the trench: 318 ± 25 yr. This paper presents an overview of the DAP system and the Puerto Rico Trench sea trials.