The following is the Jan. 5, 2021 Congressional Research Service In Focus report, A Low-Yield, Submarine-Launched Nuclear Warhead: Overview of the Expert Debate.
From the report
The Low-Yield D-5 Warhead
The Trump Administration developed a new low-yield version of the W-76 warhead for existing submarine-launched Trident II (D-5) missiles. Unclassified sources state that the existing W76-1 warhead has an explosive yield of around 100 kilotons. The National Nuclear Security Administration (NNSA) has said the low-yield version, the W76-2, would be configured “for primary-only detonation.” This could mean a yield of less than 10 kilotons.
Congress appropriated $65 million for the W76-2 warhead in FY2019 and $10 million to complete work in FY2020. It also authorized $19.6 million in FY2020 for the Navy to integrate the warhead into the submarine force. NNSA completed the first modified warhead in February 2019, began delivering warheads to the Navy by late 2019, and completed the deliveries during FY2020. The Pentagon reported in February 2020 that the Navy had begun deploying the warheads by that time. NNSA did not disclose the total number produced, although it is likely just a very small portion of the W76 stockpile (estimated, in unclassified sources, to be around 1,300 total warheads).
The Trump Administration introduced the low-yield version of the W76 warhead in the 2018 Nuclear Posture Review (NPR). It cited the need for additional “tailored” and “flexible” capabilities to address the danger of coercive nuclear use, a concept described below, by Russia and North Korea. The NPR stated that this warhead would supplement existing U.S. strategic nuclear capabilities to “enhance deterrence by denying potential adversaries any mistaken confidence that limited nuclear employment can provide a useful advantage over the United States and its allies,” and that low-yield warheads would not add to the number of deployed SLBM warheads, but would replace some “higher-yield [SLBM warheads] currently deployed.”
The NPR report, and its argument in favor of a low-yield SLBM warhead, launched a debate among U.S. experts about the rationale for the development of such a warhead and the benefits and risks that might accrue from its deployment. While some argue that this warhead is a response to Russia’s so-called “escalate to de-escalate” strategy that will strengthen deterrence and raise the nuclear threshold, others contend that it will lower the threshold for U.S. use and increase the risk of nuclear war.
Download the document here.