On January 21, 1972, the Mars 3 spacecraft observed a variation in the magnetic field during its periapsis passage over the day-side of Mars that was suggestive of entry into a Martian magnetosphere. We have obtained the original data and trajectory (Sh. Sh. Dolginov, personal communication, 1983) and have attempted to simulate the obseved variation of the magnetic field by using a gas dynamic simulation. In the gas dynamic model we first generate a flow field and then use this flow field to carry the interplanetary magnetic field through the Martian magnetosheath. The independence of the flow field and magnetic field calculation allows us to converge rapidly on an IMF orientation that would result in a magnetic variation similar to that observed by Mars 3. There appears to be no need to invole an entry into a Martian maagnetosphere to explain these observations.