NNSA uses modern tools and capabilities in the engineering sciences field which are needed to ensure the safety, security, reliability and performance of the current and future U.S. nuclear weapons stockpile. It also provides the solid and sustained engineering basis for stockpile certification and assessments that are needed throughout the entire lifecycle of each weapon.
NNSA develops capabilities to assess and improve the engineering components of both the non-nuclear and nuclear explosive package in nuclear weapons without further underground testing. Additionally, NNSA's engineering capabilities increase its ability to predict the response of all weapons components and subsystems to harsh environments (like underwater or the extreme cold of space) and the effects of aging.
Basic research and concept development are conducted by NNSA to include scientific discovery, and understanding the underlying engineering phenomena that control a weapon's performance. Assessment tools are used for new engineering phenomena introduced by changes to weapons - those that leave large uncertainties or are no longer available (e.g., loss of underground testing or closing of key experimental facilities).
NNSA is developing modern tools and capabilities essential for the success of transforming the complex to be agile for the future. This includes engineering work for the life extension programs  and efforts to consolidate special nuclear that requires the highest level of security.
NNSA's engineering focuses on four areas:
- Enhanced Surety provides "surety" (or safety, security, and control) technology so that modern nuclear surety technologies are available as options when NNSA is refurbishing or replacing nuclear weapons or parts. These modern standards were not available at the time of each weapon's original development. This ensures that new, better levels of "use-control" (or denial of unauthorized use) are achieved, and that security for nuclear weapons is consistent with modern technology and remains effective against ever-changing security threats.
- Weapon Systems Engineering Assessment Technology provides the scientific understanding, experimental capability, diagnostic development and data that are required to refurbish weapons and transform the stockpile.
- Nuclear Survivability provides the tools and technologies needed to design and qualify weapon's components and subsystems to "survive," or meet requirements to withstand radiation, space, and other hostile environments. This work includes developing hardened, or strengthened, radiation approaches and components, and modernizing tools for weapons.
- Enhanced Surveillance involves taking a weapon apart to examine how the different components have aged. This knowledge helps with decisions on how to refurbish these weapons, and with the ability to identify possible problems with the stockpile.