I did a thread about HMS Victorious a couple of weeks ago that pretty much covers a lot of the things discussed here.
HMS Victorious was commissioned as a state-of-the-art Aircraft Carrier for the Royal Navy in 1941. She went in for refit 10 years later, and because military and propulsion technology had advanced so much in that time, the refit ended up taking over 5 years and the ship was so heavily modified (even her hull was enlarged) she might as well have been a brand new vessel.
And after all that, she ended up being decommissioned just over a decade after the refit was complete due to budget cuts and changing requirements.
All the other Illustrious-class ships were scrapped just 10 years after being commissioned because the heavy damage they took in the war shortened their lifespans.
In contrast to this, HMS Hermes/INS Vikraat was a younger contemporary of Victorious that was only decommissioned in 2017 and outlasted much newer ships in service.
In short, ships have an estimated lifespan, not a set one. Some ships of the same time period might last longer than others, and there are a lot of other administrative, technological and economic factors in play that might mean they are retired early or are held in service longer than planned.
HMS Victorious was commissioned as a state-of-the-art Aircraft Carrier for the Royal Navy in 1941. She went in for refit 10 years later, and because military and propulsion technology had advanced so much in that time, the refit ended up taking over 5 years and the ship was so heavily modified (even her hull was enlarged) she might as well have been a brand new vessel.
And after all that, she ended up being decommissioned just over a decade after the refit was complete due to budget cuts and changing requirements.
All the other Illustrious-class ships were scrapped just 10 years after being commissioned because the heavy damage they took in the war shortened their lifespans.
In contrast to this, HMS Hermes/INS Vikraat was a younger contemporary of Victorious that was only decommissioned in 2017 and outlasted much newer ships in service.
In short, ships have an estimated lifespan, not a set one. Some ships of the same time period might last longer than others, and there are a lot of other administrative, technological and economic factors in play that might mean they are retired early or are held in service longer than planned.