The retired couple tell BBC Newsnight they tried to show the warship they had changed course before the shots were fired.
It comes as ex-defence secretary John Healey says the UK's enemies "do not follow timetables set by the Treasury".
The prime minister says the UK is working with other countries on a plan to protect vessels in the key waterway.
Gary Nolan spoke of the "terror" his son endured as tributes were paid at a vigil for the baby.
Three people from south Wales are arrested after £139m of cannabis shipped from Canada to UK is seized.