The skies over Germany haven't been this crowded since the second World War.

Three new budget airlines have taken off in the past three weeks, all based on Ryanair's low-cost business model. Now they hope to steal the Irish airline's customers and its crown as the biggest no-frills operator in Europe.

First to the runway was Hapag-Lloyd Express (HLX), a new airline owned by TUI, the world's largest tour operator and the owner of Ireland's Budget Travel. It has begun a huge promotional push in Germany, advertising flights "for the price of a taxi fare".

The airline's choice of hub could be a crucial point in its favour in the war with Ryanair. HLX is based at Cologne-Bonn airport, in the heart of Germany's Ruhr industrial heartland and home to more than 17 million people.

The airline is offering flights from Cologne to European cities including Paris, Rome, Milan, Barcelona, Berlin and Dresden.

"We want to be the market leader in the low-cost market in Germany," said Mr Michael Frenzel, head of HLX's parent company TUI. He said he was impressed with how Ryanair had found new customers with its pricing strategy and decided to apply it to the German market.

The average price of a HLX ticket will be €75, though the company has attracted a lot of free publicity with its fares of €19.99 on domestic flights. Although the first planes do not take off until next month, the company sold more than 50,000 tickets in its first two weeks in business, and sales are likely to increase when tickets go on sale through TUI's huge network of travel agents this month.
TUI could prove a formidable competitor for Ryanair. With a turnover of €22.4 billion, the company has deep pockets and says it is in the market for the long haul and hopes to fly more than 1.3 million people in its first year.

It has invested more than €100 million in a fleet of eight Boeing 737-700 planes operated by the German budget operator Germania, which already runs low-cost routes between Berlin, Frankfurt and Cologne.

The second big player to launch in recent weeks is Germanwings, operated by the Eurowings airline, which is partly owned by German carrier Lufthansa. With its slogan "Fly high, pay low", the company's strategy for winning customers is to make transparent the murky world of airline ticket pricing.

The company promises to sell 30 of the 128 seats on domestic flights for just €29 including all taxes on flights to 10 destinations including Madrid, Milan and even Istanbul.

Germanwings began flying at the start of this month and says it has already sold nearly 200,000 tickets. "Our goal is, through price and quality, to become the no-frills leader across Europe," said Mr Joachim Klein, the company's general manager.

The company borrows heavily from Ryanair's no-frills formula, what Germanwings calls "no schnickschnack". But like HLX, Germanwings has departed from the Ryanair formula in one crucial point: it too flies to Cologne-Bonn airport, 15km south of Cologne and connected to the city with regular shuttle buses and trains.

Ryanair's German hub is Frankfurt-Hahn airport, located more than 100km from the city of Frankfurt in the next federal state. Ryanair chose the regional airport in keeping with its company strategy of using airports with low landing charges. But the company has fought a running legal battle with Lufthansa for advertisements comparing the price of its flights from the regional airport with Lufthansa flights from Frankfurt International, one of Europe's busiest airports.

The smallest of the three newcomers to the skies over Germany is SkyEurope, operating 11 routes from its hub in Bratislava. The Slovak capital is just 50km from Vienna and the airline is marketing its service as an alternative to flying to what it calls "congested Vienna airport".

The new arrivals have revolutionised air travel in Germany in just a few short weeks, shattering the monopoly enjoyed by Lufthansa.

The national carrier has reacted to the new upstarts by offering seats on domestic flights from €88. Even the troubled German subsidiary of British Airways has adapted to the new market. Deutsche BA has relaunched itself as a budget carrier and now offers €10 fares from Berlin to Munich. Its range of cheap flights could grow next year if British operator EasyJet exercises its option to buy the airline.

"Germany is the biggest domestic air market in Europe," said Mr Ray Webster, chairman of EasyJet last May. "But it is very poorly served by low-cost airlines."

The biggest loser from the revolution in German air travel is likely to be Deutsche Bahn (DB), the national train company.

Until recently, domestic flights in Germany were prohibitively expensive, ensuring that DB had a captive customer base.

But that could change thanks to the new budget airlines and DB's new pricing system that borrows heavily from the airline industry.

Train ticket prices are no longer based on the distance travelled but on how far in advance the ticket is bought. With that, DB has abolished one of the last things rail travel had going for it, the ability to travel at short notice without being penalised.

Customers can now choose between a seven-hour train journey from Berlin to Munich that costs more than €100, or a one-hour flight for the same price.

Ryanair chief Mr Michael O'Leary says he isn't worried about Germany's new low-budget airlines. "They're very welcome but we will still remain the best value airline in Europe," he said, after announcing profits of €168.7 million for the six months to the end of September. "We are in negotiations with eight German airports and next year we will certainly fly to three or four more airports than at present."

The battle for the skies over Germany has just begun and it looks like it will be a bumpy ride.