  In the era of Extremely Large Telescopes, the current generation of 8-10m
facilities are likely to remain competitive at ground-UV wavelengths for the
foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has
been designed to provide high-efficiency (>40%) observations in the near UV
(305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of
R>20,000 (with a lower-resolution, sky-limited mode of R ~ 7,000). With the
design focusing on maximizing the instrument throughput (ensuring a Signal to
Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag
objects in 1h of observations), it will offer new possibilities in many fields
of astrophysics, providing access to key lines of stellar spectra: a tremendous
diversity of iron-peak and heavy elements, lighter elements (in particular
Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines
and the Balmer jump (particularly important for young stellar objects). The UV
range is also critical in extragalactic studies: the circumgalactic medium of
distant galaxies, the contribution of different types of sources to the cosmic
UV background, the measurement of H2 and primordial Deuterium in a regime of
relatively transparent intergalactic medium, and follow-up of explosive
transients. The CUBES project completed a Phase A conceptual design in June
2021 and has now entered the detailed design and construction phase. First
science operations are planned for 2028.
