After World War II, electric multiple units (EMUs) were produced exclusively by Pafawag from Wrocław until 1997.

[4] During this period, Polish State Railways, and later local governments, mainly purchased diesel multiple units (DMUs), as fuel-intensive locomotives dominated the operation of non-electrified lines.

One of the reasons for the failure was the high floor (1,000 mm above the railhead),[9] which hindered quick passenger exchange and the increasingly popular transport of bicycles, strollers, and wheelchairs.

[10][11][12] Pesa Bydgoszcz took this into account when designing the Elf and Acatus II, which are adapted for step-free access to platforms 550/760 mm above the railhead.

[1][13] In 2010, Pesa Bydgoszcz introduced the **Acatus II**, a modernized low-floor EMU designed for regional transportation.

These units were purchased under a European Union-funded program supporting public transportation in the Lesser Poland region.

[15] The Acatus II is a four-car, single-space, partially low-floor train designed for regional passenger transport.

All doors are located in the low-floor area, with retractable steps installed underneath to facilitate boarding from platforms lower than 550/760 mm above the railhead.

[2] The Acatus II is equipped with a driver's assistant seat,[1] allowing them to exceed speeds of 130 km/h in normal operation, which requires a two-person crew.

[17][18] On 28 January 2010, a contract was signed for the delivery of 5 new Acatus II type electric multiple units with the local government of the Lesser Poland Voivodeship.

[19] The purchase of the rolling stock was financed with European Union funds under the Lesser Poland Regional Operational Programme [pl] for 2007–2013.

On 28 January 2011, the first two trains were delivered to Kraków and made their maiden journey in the livery of Przewozy Regionalne to Tarnów and Krynica via Nowy Sącz.

According to Pesa, the reason for the rapid wear of the wheels in the EN77 is the poor state of infrastructure in the Lesser Poland Voivodeship,[21] although the manufacturer was aware of the condition of the railway lines.

[30] By **2021**, all Acatus II units underwent periodic maintenance, including modernization efforts such as **new seating, bike racks, Wi-Fi, and upgraded passenger information systems**.