A gas turbine engine (10) comprises a second compressor (14), a first compressor (16), a heat exchanger (18), a combustor (20), a first turbine (22), a second turbine (24) and a third turbine (26) arranged in flow series. The first turbine (22) is arranged to drive the first compressor (16). The second turbine (24) is arranged to drive the second compressor (14). There are means to inject liquid into the gas turbine engine (10). The means to inject liquid is arranged to inject liquid upstream (46) of the second compressor (14), within (48) the second compressor (14), between (50) the second compressor (14) and the first compressor (16), within (52) the first compressor (16), between (54) the first compressor (16) and the heat exchanger (18) or within (56) the combustor (20) to boost the power of the gas turbine engine (10). The means to inject liquid is arranged to inject liquid between (70) the combustor (20) and the first turbine (22), within (68) the first turbine (22), between (66) the first turbine (22) and the second turbine (24), within (64) the second turbine (24), between (62) the second turbine (24) and the third turbine (26), within (60) the third turbine (26) or between (72) the third turbine (26) and the heat exchanger (18) to reduce the power of the gas turbine engine (10).
