ISTANBUL—A Turkish court found more than 300 active and retired military officers guilty of plotting to overthrow the government, in a sign that the judiciary is joining a government-led effort to strip the armed forces from its once towering political influence over the country.
The decision Friday comes after more than two years of raids, detentions and hearings, with 365 people put on trial for participating in an alleged plot called Sledgehammer. Retired and active officers received as much as 20 years in prison for seeking to destabilize Turkey through clandestine agitation and prepare the grounds for a coup. The court acquitted 36 people.
Most people in Turkey see the verdict as the latest blow to the military, which once was the country's leading political player and self-appointed defender of the secular republic, established in 1923 by Mustafa Kemal Atatürk, who was also its first president.
Supporters of the government hail the decision as a victory for democracy, while others dismiss it as just another tool the Justice and Development Party, or AKP, is using to suppress opposition. The main opposition Republican People's Party, or CHP, called the case a witch hunt seeking to silence dissenters. The defendants vehemently deny the charges leveled by the state and upheld by the court.
Some analysts said the verdict calls into question relations between the civilian government and the military. They cautioned it could hurt soldiers' morale at a time when Turkey's national security is threatened by Kurdish militants seeking autonomy in the country's southeast and by the armed conflict in neighboring Syria. They said young officers might feel they are at risk of being targeted if they run afoul of the government.
"This decision seriously hurts the Turkish armed forces' morale to fight. From now on, no one will sacrifice their lives for Turkey, why should they bother?" said Atilla Ye?ilada, an Istanbul-based analyst with Global Source Partners, a political and economic research firm. "Political games are being played over the military, the biggest asset that Turkey has at hand just as it seeks to be a regional power in the Middle East."
Over the past year, clashes between Turkey and the Kurdistan Workers' Party, or PKK, have claimed more than 700 lives, according to the International Crisis Group, and Mr. Erdo?an has put his support behind rebels trying to oust Syria's President Bashar al-Assad from power.
"It's uncertain whether there can be sustainable cooperation between the government and the military to tackle national-security issues," said Robert O'Daly, a Turkey analyst at the Economist Intelligence Unit in London. "There is a need to move forward for the government and the armed forces."
Among the high-profile defendants found guilty are Gen. Bilgin Balanli, commander of the War College and the top-ranking active officer in the trial, and retired Gen. Çetin Do?an, the former commander of Turkey's First Army who was identified as the ringleader of the Sledgehammer plot.
Three generals, including Mr. Do?an, had their life sentences converted to 20 years in prison because they "only attempted" to oust Prime Minister Recep Tayyip Erdo?an's party.
Since the AKP came to power in 2002, it has been locked in a power struggle with the armed forces, the second largest in the North Atlantic Treaty Organization after the U.S.
Friday's decision is the latest sign that Mr. Erdo?an is winning the fight against the military, which has deposed four governments since 1960.
"An increasing number in the military are politically sympathetic to the AKP. And others would prefer to concentrate on being professional military officers. There is bound to be a morale effect, but it need not be terminal. Of course, a worst-case scenario is that Kemalist/secularist officers are now more generally purged as part of an Islamist long march through Turkey's institutions," said Bill Park, a senior lecturer who specializes in Turkish foreign and security policy at King's College in London. "The impression remains that this has been at least as much a political trial as a legal one."
"The people who give license to these kinds of courts, who protect them, are those that applaud injustice and lawlessness," Mr. Do?an said at the conclusion of hearings on Thursday at the trial. "May your decision be auspicious for you."
Even though the defendants plan to appeal the decision, there is little hope, said Celal Ürgen, an attorney for Mr. Do?an.
"There is no free judiciary here, on the contrary, there is a judicial system that is the backyard of the government," he said in a televised speech after the verdict was announced.
Talking to reporters in Ankara on Friday, Mr. Erdo?an said the government hopes "the just decision emerges," declining to further comment on the case because the legal process won't be completed until after the appeals ruling.
And while the prime minister has been hailed for adopting reforms to expand civil rights as part of Turkey's effort to join the European Union, he has also been criticized for jailing more journalists than China and Iran, silencing the media and using the courts to go after the opposition.
Moreover, the coup-plot trials—which include another case against an alleged clandestine organization called Ergenekon, composed of journalists, military officers and academics—have come under great scrutiny for what analysts have called flimsy evidence.
Indeed, expert reports from the U.S. and Turkey have shown that the evidence at the heart of the prosecutors' Sledgehammer case—a CD that contains key documents—is fraudulent. The findings state that Microsoft Word, Excel and PowerPoint documents purportedly dating to 2002-2003 were prepared with fonts and in formats that the Seattle-based company didn't unveil until 2007. Furthermore, some of the documents dated 2003 refer to companies established in 2008 and 2009.
The Sledgehammer indictment outlines an alleged plot involving attacks, such as bombings of mosques in Istanbul to create an atmosphere of chaos and instability. That, prosecutors argued, would provide grounds for military intervention in civilian politics.
Court documents state the coup plan was rehearsed during an annual army seminar in 2003, in which one of the war-game scenarios was against an "internal Islamist threat" in Turkey. Officers at the trial said the presentations at the seminar weren't coup plans, but rather war games.
"The verdict will not be made about us, it will be made against the Turkish armed forces," Gen. Balanli said before the decision.
The traditionally secular military has always viewed the AKP government with deep suspicion. At the root of it is the AKP's formation in 2001, when old hands from the Welfare Party decided to chart a more moderate course than Turkey's leading Islamist party. Welfare was shuttered by a 1998 court decision for violating the secularism principle in the constitution. A year earlier, Welfare's coalition government collapsed following a decree from the soldiers.
In a 2010 interview with The Wall Street Journal before the trial, Mr. Do?an criticized Western countries for believing that "mild Muslims" can lead Turkey to democracy. He said, "Once [the AKP] have power all to themselves, they will turn Turkey into Iran, step by step. I see it going there."