Aero L-39 Albatros L-39ZO

The L-39ZO was the first Albatros version designed from the outset to carry weapons. The sources disagree on what the letters mean: the English, Spanish and German Wikipedias read the Z as zbraně, "weapons", while the Czech one interprets ZO as Zahraniční Obchod, "foreign trade". Both readings point to the same thing: a weapons trainer conceived for export, which the English Wikipedia describes as an interim variant pending the more complete L-39ZA.

The road to the ZO ran through three prototypes, X-09, X-10 and X-11, built between 1973 and 1976 as a common basis for both the ZO and the ZA; according to the German Wikipedia, their test programme was completed in 1977. The version's first flight is dated 25 June 1975.

Compared with the L-39C, the changes are mainly structural. The wing is strengthened and gains four hardpoints: the inboard pair stressed for 500 kg and the outboard pair for 250 kg, for a total external load of 1,150 kg, while the landing gear is modified for the higher weights. The German Wikipedia details the weapons fit: bombs of up to 500 kg, UB-16-57 pods with 16 unguided S-5 rockets each, auxiliary tanks of 150 litres on the outboard stations and 350 litres on the inboard ones, guided air-to-air missiles and 7.62 or 12.7 mm machine-gun pods. In the reconnaissance role it usually flew with a camera pod on the left inboard station and a 350-litre tank on the right. Unlike the ZA, the ZO lacked the ventral GSh-23 cannon pod and that version's even sturdier landing gear.

The first deliveries went to Iraq in 1977; Iraq was also the first export customer for the L-39 and, according to the English Wikipedia's list of operators, received 59 L-39ZOs alongside 22 L-39Cs. The largest buyer was Libya, which acquired some 180 around 1978 (181 according to the list of operators and the German Wikipedia). They served at the Sabha and Okba Ben Nafi flying schools, alongside Yugoslav G-2 Galebs for advanced jet training and Italian SF.260s for primary training. Libya's L-39s were deployed in the conflict with Chad, mainly at Ouadi Doum air base; in the final Chadian offensive of March 1987, Chad captured the base and, according to its report to the UN, seized 11 L-39s and destroyed or downed at least four. The list of operators credits Chad with 11 L-39ZOs, although the sources consulted do not explicitly link the two facts, and records ten former Libyan ZOs delivered to Egypt.

Syria bought 55 L-39ZOs and 44 L-39ZAs from Czechoslovakia in the 1970s and 1980s. In the German Democratic Republic, the air force of the National People's Army received 52 ZOs (50 according to the English Wikipedia) plus two L-39Vs, and flew them with the FAG-25 training regiment at Bautzen. A ZO in service since 28 November 1977 was lost there on 12 June 1989 near Anklam: the engine failed because of clogged oil filters, and the two crew members steered the aircraft away from a built-up area before ejecting too late to survive. The fleet was withdrawn in 1990, and twenty former East German ZOs went to the Hungarian Air Force.

Other users included Ghana, with two aircraft, and Mozambique, which acquired one from Romania in 2013. Examples survive today in museums and private hands, such as the one displayed at the Technik Museum Speyer hotel and serial number 2314, kept airworthy at the Olympic Flight Museum in Olympia, Washington. In total, 337 L-39ZOs were built.