On January 20, 2015 the Coast Guard of the USA formally declared its SOLAS (Safety of Life at Sea) compliant Sea Area A1 designation. According to SOLAS regulations, the definition of Sea Area A1 is:
Sea Area A1 means an area within the radiotelephone coverage of at least one VHF Coast Station in which continuous Digital Selective Calling (DSC) alerting is available, as may be defined by a Contracting Government.
The completion of the coastal portion of the RESCUE 21 project has enabled the USA to be able to comply with this SOLAS definition and declare a Sea Area A1. The defined Sea Area A1 has some exclusions:
The Coast Guard is declaring Sea Area A1 in certain areas off the coast of the United States based upon the performance of the Coast Guard's Rescue 21 System, and in accordance with applicable provisions of the International Convention for the Safety of Life at Sea, 1974 (SOLAS). The Coast Guard defines Sea Area A1 as those areas where more than ninety percent of the area within 20 nautical miles seaward of the territorial baseline along the East, West and Gulf Coasts of the United States, excluding Alaska, and including Hawaii, Puerto Rico, Guam, the Virgin Islands of the United States, and the Northern Mariana Islands of Saipan, Tinian, and Rota, is within coverage of Coast Guard very high frequency (VHF) Coast Stations that provide both a continuous watch for Digital Selective Calling (DSC) distress alerts on Channel 70 and a capability to respond to distress alerts.
Now I will expand a bit on this prior mention of Sea Area 1. First I will excerpt the definition without so many exemptions appended to it:
The Coast Guard defines Sea Area A1 as those areas where more than ninety percent of the area within 20 nautical miles seaward of the territorial baseline along the East, West and Gulf Coasts of the United States...is within coverage of Coast Guard very high frequency (VHF) Coast Stations....
The full announcement then comments:
Based upon the demonstrated coverage and performance of the Rescue 21 System, and upon the applicable requirements of SOLAS, the Coast Guard is declaring as Sea Area A1 those areas within 20 nautical miles seaward of the territorial baseline along the East, West, and Gulf coasts of the United States...
Complete details from the Federal Register are found at:
https://www.federalregister.gov/articles/2015/01/20/2015-00798/declaration-of-sea-area-a1