A member of a police department who served in the military establishment of the United States during a period of national emergency immediately following service as a member of the police department, shall not be required to contribute to the police pension fund by salary deduction or otherwise for the period covered by his military service, but in computing the length of service of a member of a police department for the purpose of determining eligibility for retirement, the period of military service, as prescribed by this section, shall be included.