Four Airbus A321 will grow the group airline short- to medium-haul fleet to 105 aircraft for summer 2019.
Cook aircraft are based variously across the UK, Scandinavia, Spain and Germany.
The other three A321s joining the Cook fleet will be stationed in Germany.
Two of the A321s will go to Condor to operate its summer 2019 schedule. These aircraft will then be transferred to the UK for the winter.
Cook says its fleet growth would support “operational stability during high season”.
"Using additional aircraft of our own is another measure to live up to our quality promise next summer, even during the high season," said Christoph Debus, Cook’s chief airline officer.
The new aircraft will make more jobs available, with the airline recruiting for new personnel “on the ground and in the air”.
The news comes despite Cook intimating its entire group airline is up for sale.
The operator embarked on a “strategic review” of its airline last month after reporting an increase in underlying operating loss of £14 million to £60 million and a post-tax loss of £163 million for 2018.
