As the partisan fight over mail-in voting intensifies ahead of the November presidential election, hundreds of thousands of U.S. troops and their families are preparing, as they have for decades, to cast absentee ballots by mail.

Defense Department officials say the delivery of ballots cast by troops at military installations across the United States and far-flung locations around the globe should not be significantly affected by recent U.S. Postal Service changes and an expected crush of mail-in voting because of the coronavirus pandemic.

According to Peter Graeve, chief of plans and policy for the Military Postal Service Agency (MPSA), ballots completed by service members, their family members and military contractors overseas between Sept. 1 and Dec. 8 will receive a USPS express mail label for expedited handling.

The average transit time to voting centers in the United States — whether ballots are sent from giant citylike bases in Germany or tiny outposts in the Syrian desert — should be six days, Graeve said.

But a Pentagon office dedicated to facilitating voting for troops and other Americans overseas has cautioned that remote voting could be more complicated this year.

“Communication with the voter is more important now than ever,” the Federal Voting Assistance Program (FVAP) said in a recent covid-19 update on its website, urging election officials to communicate potential options to voters to ensure that ballots arrive in time. “Due to international airport interruptions, many military and overseas voters will face greater-than-normal challenges with returning mail back to the United States in a timely fashion,” it said.

Lisa Lawrence, a Pentagon spokeswoman, said mail, including ballots, had “continued to move to overseas military personnel regardless of international postal disruptions.”

But, she added, “slight delays have occurred and the Military Postal Service Agency continues to monitor conditions globally with specific attention given to balloting materials.”

The military’s ability to ensure that service members can successfully vote is under heightened scrutiny as the U.S. Postal Service warns that some of the ballots Americans cast by mail may not arrive in time to be counted.

President Trump has repeatedly spoken out against mail-in voting and said he is against additional funding for the Postal Service because it could support voting by mail.

Military personnel, including those who are located within the United States but outside their state of residence, have been taking part in U.S. elections on an absentee basis since as early as the War of 1812 and, in greater numbers, the Civil War, according to the National Postal Museum.

In the 2016 election, service members and their families sent more than 633,000 ballots to their home jurisdictions. About 20,000 of those were rejected, half because they weren’t received in time. The number of absentee ballots sent to service members and their families increased by nearly a quarter between the 2012 and 2016 elections.

The successful delivery of those ballots to voting centers relies on a vast logistical operation overseen largely by the MPSA, which is run by the Army but provides service for all troops and their families overseas.

According to an overview provided by MPSA, mail processed at the service’s network of overseas post offices is taken by commercial or military aircraft to military mail terminals, then flown by commercial or military aircraft to airports or bases in the United States.

A defense official said service members stationed in Afghanistan, for example, would take their ballot to the base post office, where they would not be charged for express mail handling. The ballot, along with other mail, would then be taken to Bagram air base, the main air hub for foreign forces in the country, where it would be loaded on the next commercially contracted flight. After a likely layover in Bahrain, the mail would arrive in New York, where it would be handed over to the Postal Service, the official said, speaking on the condition of anonymity because he was not authorized to speak publicly.

The Postal Service picks up military mail flown to U.S. bases, but commercial air carriers transport the military mail they handle to Postal Service processing facilities. In both cases, the mail — including service members’ ballots — is then moved onward as part of the Postal Service’s mail chain.

Service members voting in some states and jurisdictions can sidestep that process and submit their absentee ballot by fax or email, if permitted by their state or jurisdiction.

Before any of that can happen, they must ensure they are registered to vote and request an absentee ballot, which can be done by different means according to their state or territory.

Lawrence said service members are briefed on voting before being deployed overseas.

“This affords an opportunity for personnel to complete a Federal Post Card Application prior to deployment,” she said, or submit a write-in ballot depending on the length of their deployment.

Officials said service members have the option of filling out a write-in “backup” ballot if their requested ballot does not arrive in time, which can be submitted according to rules of their voting jurisdiction.