A safety and arming unit with a safe separation distance device (14),
which acts as a function of a free-flight incident flow and temperature,
for the fuze (12) of a projectile (11), which fuze is hermetically sealed
from environmental influences, has, as a measurement device for the
cooling, as a function of the incident flow, of a conductor through which
current passes, in the heating circuit (18) of a resistant heating
element (16) which is fitted flat on the fuze casing surface (17), an
electronic current measurement apparatus (21) which is connected upstream
of an evaluation circuit (22), in order to ram a firing circuit. Two
heating elements (16, 16''), which are fed in the same way, are
preferably arranged one behind the other in the incident flow direction
(15), and, additionally as an environmental temperature sensor, a
comparison heating element (16') which is not influenced by the incident
flow (15). This results in a reliable safe separation distance, even for
slow projectiles (11), without adversely affecting their aerodynamic
behaviour and independently of the environmental atmosphere.