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In addition, it's not immediately clear whether the M1s for Ukraine will be entirely new production tanks or if they will come through some other source. The U.S. Army has thousands of older Abrams in storage that a contractor could be hired to refurbish to a like-new condition or that could be used as donors to help with the construction of tanks that use a mixture of new and remanufactured components.
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The armor issue will put limits on how fast the U.S. government can supply any Abrams to Ukraine, whatever the source for those tanks might be. Even if the M1s for Ukraine are pulled from storage and rebuilt, it's far more likely than not that they will have armor packages that will need changing. This is a complex process, as evidenced by recent publicly available contract documents related to the sale of Abrams tanks to Poland.
Poland's future fleet of M1A2 SEPv3 Abrams tanks will include examples that feature refurbished M1A1 turrets. As part of the sale, the U.S. Army is facilitating the installation of a Foreign Military Sales-approved armor package onto those turrets.
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With all this in mind, it remains to be seen how American officials might seek to mitigate these issues as part of the transfer of Abrams tanks to Ukraine. It also raises the question of whether it might be possible to acquire export variants that already have downgraded armor and other systems from other countries. The U.S. government's use of USAI funds to help pay for the refurbishment of Soviet-designed T-72B tanks acquired from third parties for Ukraine last year provides an eye into how this might be done.
The two largest foreign operators of the Abrams are Egypt and Saudi Arabia. The Egyptian Army has around 1,360 M1A1s, at least on paper. The Saudi armed forces have some 370 more, 170 of which are reportedly in storage, according to the 2016 edition of The Military Balance from the International Institute for Strategic Studies (IISS).
Egypt and Saudi Arabia are both major partners of the United States. At the same time, however, both countries have, at best, complicated relations with Russia. So, it could be very hard to convince either of them to help in this endeavor due to the very real risk of upending their ties with Moscow.