Gas turbines if used correctly have big advantages over diesels, with their compactness, very high power density, quietness, acceleration and low start-up time, BUT a GT is most efficient at maximum power output, at lower rotational speed the pressure of the compressed air drops and thus thermal and fuel efficiency drop dramatically and they become gas guzzlers.
The Zumwalt IEP design after experiance with the T45, use four GTGs (two MT30 plus Curtis-Wright generator and two MT7/RR4500 GTG), so ship with its electric grid can run one to four GTGs as required by load on system and GTs run at their maximum output/fuel efficiency, the grid powering the two propellers and sensors/weapons/hotel load. A refinement so as not to keep a spare GTG running as necessary backup in case of short out (it takes a short time to bring spare GTG online), is the use of a UPS, uninterruptible power supply, to give near instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors or flywheels, eg RRS Sir David Attenborough uses SAFT Li-ion batteries to provide 1450 kWh, RR Marine AS claiming 5 MW peak effect available.
The Zumwalt IEP is a sophisticated and fuel efficient system for a warship and may be an ideal solution to accommodate large and highly volatile loads but its expensive, that's why hybrid electric drive, HED (mainly with diesels as less costly than GTs), has become popular as it marries most of the benefits of IEP with mechanical propulsion.
Many, many examples of new ships running HED i.e. Japanese 25DD; Korean Daegu; Italian FREMM & PPA; USCG OPC; Tide class; Type 26 (not sure if Sir David Attenborough is HED or IEP).
Another example is the Damen Sigma 10514 CODOE where to bring the benefits of HED costs minimised to make it a viable option compared to mechanical propulsion plus separate DGs, HED normally carries a premium cost of ~60%, have posted before. Damen HED use two Spanish Indar 1,325 kW electric motors with two water-cooled variable frequency drives with active front ends powered by its DGs. VFD's cooled by one water cooling unit to save weight, space, cost and connected to the vessel’s power grid without the use of a transformer also saving big on weight, space and cost. Normally direct (conductive) coupling can cause unwanted effects on sensitive operational equipment connected to the grid, with the new tech, Bakker Sliedrecht smart filter, mitigates the disturbance levels in order to comply with the IEC and Navy regulations, plus selective earth fault detection.